Screening Assessment for the Challenge

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Zinc, bis[O,O-bis(1,3-dimethylbutyl) phosphorodithioato-S,S']-, (T-4)-

Chemical Abstracts Service Registry Number
2215-35-2

Environment Canada
Health Canada

July  2010

(PDF Version 376 KB)

1. Synopsis
2. Introduction
3. Substance Identity
4. Physical and Chemical Properties
5. Sources
6. Uses
7. Releases to the Environment
8. Environmental Fate
9. Persistence and Bioaccumulation Potential
10. Potential to Cause Ecological Harm
11. Potential to Cause Harm to Human Health
12. Conclusions
13. References
14. Appendix 1: Robust Study Summary
15. Appendix 2: Estimated concentrations of zinc BDBP in environmental media using ChemCAN version 6.00 (ChemCAN 2003)
16. Appendix 3: Estimates of total and media-specific daily intakes of zinc BDBP for various age groups
17. Appendix 4: Dermal exposure estimate for a do-it-yourself motor oil change
18. Appendix 5: Summary of (Q)SAR Results for Zinc BDBP
19. Appendix 6: PBT Model Inputs Summary Table

Synopsis

Pursuant to section 74 of the Canadian Environmental Protection Act, 1999 (CEPA 1999), the Ministers of the Environment and of Health have conducted a screening assessment on Zinc, bis[O,O-bis(1,3-dimethylbutyl) phosphorodithioato-S,S']-, (T-4)- (zinc BDBP), Chemical Abstracts Service Registry Number 2215-35-2. This substance was identified as a high priority for screening assessment and included in the Challenge because it had been found to meet the ecological categorization criteria for persistence, bioaccumulation potential and inherent toxicity to non-human organisms and is believed to be in commerce in Canada .

The substance zinc BDBP was not considered to be a high priority for assessment of potential risks to human health, based upon application of the simple exposure and hazard tools developed by Health Canada for categorization of substances on the Domestic Substances List. Therefore, this assessment focuses on information relevant to the evaluation of ecological risks.

Zinc BDBP is an organometallic dialkyldithiophosphate substance that is used in Canada and elsewhere as an anti-wear oil additive. It also acts as an antioxidant. The substance is not naturally produced in the environment. Between 10 000 and 100 000 kg of zinc BDBP were imported into Canada in 2005 and between 100 000 and 1 000 000 kg were imported in 2006 for use in the petroleum industry. The quantity of zinc BDBP imported into Canada indicates that it could be potentially released to the Canadian environment.

Based on reported use patterns and certain assumptions, most of the substance is transformed during use. Small proportions are estimated to be released to wastewater (1.9%) and to paved/unpaved land surfaces (0.9%). Zinc BDBP is somewhat soluble in water, is not volatile and has a tendency to partition to particles and lipids (fat) of organisms because of its hydrophobic nature. For these reasons, zinc BDBP will be likely found mostly in sediments and soil, and to a minor extent, in water. It is not expected to be significantly present in air. It is also not expected to be subject to long-range atmospheric transport.

Based on its physical and chemical properties, zinc BDBP is expected to be persistent in in water, soil and sediments. New bioaccumulation predictions suggest that this substance has a low potential to accumulate in the lipid tissues of organisms. The substance therefore meets the persistence criteria but does not meet the bioaccumulation criteria as set out in the Persistence and Bioaccumulation Regulations.

For this screening assessment, a moderately conservative industrial exposure scenario was selected in which an operation discharges zinc BDBP into the aquatic environment. The predicted environmental concentration in water (PEC) was below the predicted aquatic no-effect concentration (PNEC) calculated from a Species Sensitivity Distribution (SSD) using data from other substances within the dialkyldithiophosphate category. Additionally, results from a consumer release scenario, that estimates exposure ( PECs) resulting from the down-the-drain release using conservative assumptions, indicate that the PNEC is unlikely to be exceeded. Consequently, exposure levels are not likely to exceed the aquatic PNEC in the conservative scenarios considered, whether based on consumer or industrial releases; that is, conservative risk quotients are almost always below 1.

Based on the information available, it is concluded that zinc BDBP is not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends.

The potential for exposure of the general population to zinc BDBP from environmental media is expected to be negligible. However, there is potential for dermal exposure from its use as a motor oil additive, which is typically used in an occupational setting, but may also be used directly by consumers.

The toxicological dataset for zinc BDBP is limited. However, health effects associated with zinc BDBP dermal exposure in experimental animals include dermal irritation, body weight loss, elevated white blood cell count and at higher exposure levels, effects on testes.

The margins between upper-bounding estimates of exposure from environmental media and consumer products (additive in motor oil) and levels associated with effects in experimental animals are considered to be adequately protective. It is thus concluded that zinc BDBP is not entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.

Based on the information available, it is concluded that zinc BDBP does not meet any of the criteria set out in section 64 of the Canadian Environmental Protection Act, 1999.

This substance will be considered for inclusion in the Domestic Substances List inventory update initiative. In addition and where relevant, research and monitoring will support verification of assumptions used during the screening assessment.

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Introduction

The Canadian Environmental Protection Act, 1999 (CEPA 1999) (Canada 1999) requires the Minister of the Environment and the Minister of Health to conduct screening assessments of substances that have met the categorization criteria set out in the Act to determine whether these substances present or may present a risk to the environment or to human health.

Based on the information obtained through the categorization process, the Ministers identified a number of substances as high priorities for action. These include substances that

• met all of the ecological categorization criteria, including persistence (P), bioaccumulation potential (B) and inherent toxicity to aquatic organisms (iT), and were believed to be in commerce in Canada ; and/or
• met the categorization criteria for greatest potential for exposure (GPE) or presented an intermediate potential for exposure (IPE), and had been identified as posing a high hazard to human health based on classifications by other national or international agencies for carcinogenicity, genotoxicity, developmental toxicity or reproductive toxicity.

The Ministers therefore published a notice of intent in the Canada Gazette, Part I, on December 9, 2006 (Canada 2006a), that challenged industry and other interested stakeholders to submit, within specified timelines, specific information that may be used to inform risk assessment, and to develop and benchmark best practices for the risk management and product stewardship of those substances identified as high priorities.

The substance Zinc, bis[O,O-bis(1,3-dimethylbutyl) phosphorodithioato-S,S']-, (T-4)- had been identified as a high priority for assessment of ecological risk because it had been found to be persistent, bioaccumulative and inherently toxic to aquatic organisms and was believed to be in commerce in Canada.

The Challenge for this substance was published in the Canada Gazette on January 31, 2009 ( Canada 2009a). A substance profile was released at the same time. The substance profile presented the technical information available prior to December 2005 that formed the basis for categorization of this substance. As a result of the Challenge, a submission of information pertaining to the bioaccumulation potential of the substance was received.

Although Zinc, bis[O,O-bis(1,3-dimethylbutyl) phosphorodithioato-S,S']-, (T-4)- was determined to be a high priority for assessment with respect to the environment, it did not meet the criteria for GPE or IPE and high hazard to human health based on classifications by other national or international agencies for carcinogenicity, genotoxicity, developmental toxicity or reproductive toxicity. Therefore, this assessment focuses principally on information relevant to the evaluation of ecological risks.

Screening assessments focus on information critical to determining whether a substance meets the criteria as set out in section 64 of CEPA 1999. Screening assessments examine scientific information and develop conclusions by incorporating a weight-of-evidence approach and precaution.^[1]

This screening assessment includes consideration of information on chemical properties, hazards, uses and exposure, including the additional information submitted under the Challenge. Data relevant to the screening assessment of this substance were identified in original literature, review and assessment documents, stakeholder research reports and from recent literature searches, up to June 2009 for the physical and chemical properties, and exposure and ecological effects sections of the document. Key studies were critically evaluated; modelling results may have been used to reach conclusions.

When available and relevant, information presented in hazard assessments from other jurisdictions was considered. The screening assessment does not represent an exhaustive or critical review of all available data. Rather, it presents the most critical studies and lines of evidence pertinent to the conclusion.

This screening assessment was prepared by staff in the Existing Substances Programs at Health Canada and Environment Canada and incorporates input from other programs within these departments. The ecological and human health portions of the assessment have undergone external written peer review/consultation. Additionally, the draft of this screening assessment was subject to a 60-day public comment period. While external comments were taken into consideration, the final content and outcome of the screening risk assessment remain the responsibility of Health Canada and Environment Canada. Approaches used in the screening assessments under the Challenge have been reviewed by an independent Challenge Advisory Panel.

The critical information and considerations upon which the assessment is based are summarized below.

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Substance Identity

Substance name

For the purposes of this document, this substance will be referred to as zinc BDBP, derived from the DSL inventory name: Zinc, bis[O,O-bis(1,3-dimethylbutyl) phosphorodithioato-S,S'], (T-4)-.

Table 1. Substance identity for zinc BDBP

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Physical and Chemical Properties

A number of models have been re-run for this SAR owing to (1) the availability of updated information on physical and chemical properties; and (2) identification of a different structure for zinc BDBP than the one that was used for the previously published substance profile. The structure used in the profile was incorrect as one half of the structure bonded to the zinc was missing.

Table 2 contains experimental and modelled physical and chemical properties of zinc BDBP that are relevant to its environmental fate. Note that this substance is expected to persist and not to transform nor dissociate in water (See fate and persistence sections). Therefore, physical and chemical properties of the substance apply to the parent molecule form of the substance.

Table 2. Physical and chemical properties for zinc BDBP

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Sources

Zinc BDBP is not reported to occur naturally. According to the raw data submitted under the Challenge, for the year 2006 in Canada , no manufacture of zinc BDBP was reported (Environment Canada 2009a). However, two companies reported importing a total quantity between 100 000 and 1 000 000 kg (Environment Canada 2009a). For the year 2005 in Canada , no manufacture of zinc BDBP was reported ( Canada 2006b). However, two companies reported importing a total quantity between 10 000 and 100 000 kg of zinc BDBP into Canada ( Canada 2006b).

Products containing zinc BDBP may enter the country even if they are not identified as such in the section 71 survey because they may be imported unknowingly in manufactured items, or in quantities below the 100 kg reporting threshold for the survey.

Elsewhere, zinc BDBP has been identified as an International Council of Chemical Associations high production volume (HPV) chemical (ICCA 1999), an Organisation for Economic Co-operation and Development HPV chemical (OECD 2004), and as a United States HPV chemical (Zinc Dialkyldithiophosphate Category) (US EPA 2008). According to 1986-2002 information from the United States Environmental Protection Agency (US EPA 2009), the U.S. import/production was in the range of 454–4545 tonnes in 1986, 1990, 1994 and 2002. In 1998, the import/production was in the range of 4545–22 727 tonnes. In Sweden and Denmark , total use was 17–21 tonnes annually from 1999 through 2005, but dropped sharply to roughly 1 tonne annually in 2006 and 2007 (SPIN 2009).

Given the use of this substance in other countries, it is probable that the substance is entering the Canadian market as a component of industrial and/or consumer products. Available information is currently not sufficient to derive a quantitative estimate of the importance of this possible source.

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Uses

Information on uses for the 2005 and 2006 calendar years was gathered in response to notices published under S.71 of CEPA 1999 ( Canada 2006b; 2009b). Companies identified themselves as primarily engaged in refining crude petroleum; manufacturing petroleum products (including blending and compounding lubricating oils and greases from refined petroleum products and re-refining used products); and manufacturing miscellaneous chemical products.

The above industrial activities identified through the CEPA 1999 section 71 notice are based on the North American Industry Classification System (NAICS) codes. Over 3000 NAICS codes have been defined. NAICS codes describe a company’s sectors and business lines without, however, specifying the exact use of the substance or product within the company. NAICS codes differ from the functional use codes used for DSL nomination information in that functional use codes indicate specific applications or uses for the substance or products containing the substance.

Information on the use of this substance that was received through the notice indicates that zinc BDBP could be used in Canada in a dispersive manner.

Potential uses in Canada

The information below on potential uses of zinc BDBP was found through searches of the available scientific and technical literature.

In Canada , zinc BDBP is used in lubricity additive packages that may be added to form finished oils such as motor oil (ACC 2005; Environment Canada 2009a; Ford Motor Company 2002, 2005). According to the US EPA (2008), more generally, zinc dialkyldithiophosphates are used to formulate finished lubricating oils including all types of automotive and diesel engine crankcase oils, industrial oils and hydraulic fluids. They are used as anti-wear inhibitors to reduce wear in engines and hydraulic equipment parts, and also act as antioxidants. In Nordic countries, zinc BDBP is used industrially in the categories of lubricants/additives and base oils. More specifically, the substance is used in the manufacture, maintenance and repair of motor vehicles and motorcycles and in manufacture of automotive fuel (SPIN 2009). Zinc BDBP is believed to be added to motor oil as an extreme pressure additive, although it may serve as a corrosion inhibitor or anti-wear additive (Danish Environmental Protection Agency 2005).

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Releases to the Environment

Responses to a notice issued under section 71 of CEPA 1999 indicated no reported releases of zinc BDBP to the environment in the 2006 calendar year (Environment Canada 2009a). Zinc BDBP is not a reportable substance to the National Pollutant Release Inventory (NPRI 2008) or to the U.S. Toxics Release Inventory (TRI 2007); therefore no release data were available from these sources.

The losses of zinc BDBP via various routes during its life cycle are estimated based on regulatory survey data, industry data and data published by different organizations. The losses are grouped into six types: (1) discharge to wastewater; (2) emission to air; (3) loss to paved/unpaved surfaces; (4) chemical transformation; (5) disposal to landfill; and (6) disposal by incineration. Losses may occur at one or more of the substance’s life cycle stages that include manufacture, industrial use, consumer/commercial use, and disposal. To assist in estimating these losses, a spreadsheet (Mass Flow Tool) was used that incorporates all data and assumptions required for the estimation (Environment Canada 2009c). Unless specific information on the rate or potential for release of the substance from landfills and incinerators is available, the Mass Flow Tool does not quantitatively account for releases to the environment from waste disposal sites.

In the context of the estimation assisted by the Mass Flow Tool, the discharge to wastewater refers to raw wastewater prior to any treatment, either on-site industrial wastewater treatment or off-site municipal sewage treatment. In a similar manner, the loss via chemical transformation refers to changes in substance identity that occur within the manufacture, industrial use, or consumer/commercial use stages, but excludes those during waste management operations such as incineration and wastewater treatment.

The losses estimated for zinc BDBP over its life cycle are presented in Table 3 (Environment Canada 2009c). The substance is expected to be released to wastewater at 1.9% of the total quantity used in Canadian commerce. In general, loss to wastewater is a common source for releases to water through wastewater treatment facilities and to soil through application of biosolids. Most losses to wastewater are expected to result from consumer use.

Table 3. Estimated losses of zinc BDBP during its life cycle

Zinc BDBP is also expected to be released to the environment via routes other than wastewater. There are various mechanisms for the loss to paved/unpaved land surfaces such as leaks and spills. The substance lost to paved/unpaved surfaces can be blown to nearby soil or washed into sewers, resulting in releases to water and soil. The substance entering recycling facilities can find its way to water and/or soil, depending upon the operational characteristics of these facilities. The substance disposed of in landfill has a low potential to leach out into groundwater.

The above loss estimates indicate that zinc BDBP has a moderate potential for release to the environment.

This substance is also likely present in similar consumer products that are imported into Canada . Although available information is currently not sufficient to estimate the total volume released to the environment or sent for waste and wastewater management from the latter sources, it is anticipated that the proportions lost to each receiving medium would not be significantly different.

In summary, releases of zinc BDBP occur primarily during consumer use (leaks, spills during use, improper disposal) and, to a lesser extent during industrial handling, blending and repackaging.

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Environmental Fate

The substance zinc BDBP is not expected to dissociate in water based on (1) its resistance to hydrolysis (see persistence section below); (2) the rather strong level of covalence (81%) of the bond between zinc and sulphur which likely confers high stability, indicating a negligible potential for dissociation of zinc from the molecule (the percentage covalence was calculated from the difference in electronegativity between the zinc and sulphur atoms); and (3) the level of aquatic toxicity that would be higher if there had been evidence of the liberation of significant amounts of dissolved zinc. ^[2] Therefore, in water bodies at environmentally relevant pH (6–9), zinc BDBP is expected to be undissociated, which indicates that the biotic exposure to zinc BDBP will be from the neutral chemical. This also indicates that partitioning behaviour predicted using the log K_ow, log K_oa and log K_oc is appropriate.

Based on its physical and chemical properties (Table 2), the results of Level III fugacity modelling (Table 4) suggest that zinc BDBP is expected to predominantly reside in soil and/or sediment, depending on the compartment of release.

Table 4. Results of the Level III fugacity modelling (EQC 2003)

If released to air, a very low amount of the substance is expected to reside in air (see Table 4 above). Based upon the low vapour pressure of 1.17 x 10^-4 Pa and low Henry’s Law constant of 1.49 x 10^-2 Pa·m³/mol, zinc BDBP is non-volatile. Therefore, if released solely to air, it will not tend to remain in this compartment; but rather the substance will partition mainly to soil (~ 79%) and to a lesser extent to sediment (~ 20%) (see Table 4 above).

If released to water, zinc BDBP is expected to strongly adsorb to suspended solids and sediment based upon a very high estimated log K_oc value of ~ 7. Volatilization from water surfaces is expected to be an unimportant fate process based upon this compound’s estimated Henry’s Law constant. Thus, if water is the receiving medium, zinc BDBP is expected to mainly partition into sediment (see Table 4).

If released to soil, zinc BDBP is expected to have high adsorptivity to soil (i.e., expected to be immobile in this environmental compartment) based upon its estimated log K_oc. Volatilization from moist soil surfaces seems to be an unimportant fate process based upon its estimated Henry’s Law constant. This chemical is not expected to volatilize from dry soil surfaces based upon its vapour pressure. Therefore, if released to soil, zinc BDBP will entirely reside in this environmental compartment, which is illustrated by the results of the Level III fugacity modelling (see Table 4).

As explained in footnote to Table 4 above, based on a more realistic scenario that takes into account the relative proportions likely to be lost to wastewater and soil most of the substance will partition to sediment (79.8%), followed by soil (18.8%) and water (1.4%).

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Persistence and Bioaccumulation Potential

Environmental Persistence

Table 5a presents empirical persistence values that were found for two analogue substances in the zinc dialkydithiophosphate category. The closest analogue of zinc BDBP is CAS RN 84605-29-8, Phosphorodithioic acid, mixed O,O-bis(1,3dimethylbutyl and isopropyl) esters, zinc salts (US EPA 2008). This substance was considered closest based on the fewest differences in the number of carbons in the 4 chains and also because it has the nearest molecular weight. A substance in the same category but less related was also considered, CAS RN 54261-67-5, Phenol, dodecyl-, hydrogen phosphorodithioate, zinc salt. The ready-biodegradation studies (Modified Sturm Test, OECD 301B), for both substances, show relatively low (4.2- 5.9%) biodegradation of the substances over 28 days (Table 5a). The values are based on carbon dioxide evolution. These tests indicate that the half-life in water is likely to be longer than 182 days (6 months) and that the substances are therefore likely to persist in that environmental compartment.

Table 5a. Empirical analogue data for degradation of zinc BDBP

Since few experimental data on the degradation of analogues of zinc BDBP are available, a quantitative structure-activity relationship (QSAR)-based weight-of-evidence approach (Environment Canada 2007) was also applied using the degradation models shown in Table 5b below. The BIOWIN models and others were used to estimate the substances’ persistence in water, and these predictions were extrapolated to soil and sediment, the compartments to which zinc BDBP is expected to primarily partition when released to the environment. Zinc BDBP contains functional groups (dithiophosphate esters) expected to undergo very slow hydrolysis.

Table 5b summarizes the results of available QSAR models for degradation in air and water.

Table 5b. Modelled data for degradation of zinc BDBP

In air, a predicted atmospheric oxidation half-life value of 0.034 days (see Table 5b above) demonstrates that this substance is likely to be rapidly oxidized in air. The compound is not expected to react (or react appreciably) with other photo-oxidative species in the atmosphere, such as O₃; nor is it likely to degrade via direct photolysis. Therefore, it is expected that reactions with hydroxyl radicals will be the most important fate process in the atmosphere for zinc BDBP. With a half-life of 0.034 days via reactions with hydroxyl radicals, zinc BDBP is considered not persistent in air.

The five biodegradation models suggest that biodegradation is not fast and that the half-life in water would be = 182 days (Environment Canada 2009b). The models consider primary biodegradation and ultimate degradation. The prediction from CPOPs is considered to be more reliable than the prediction from BIOWIN because of the slightly better and larger model training set coverage. The prediction from CPOPs suggests a very slow rate of biodegradation. The substance also contains two structural features associated with chemicals that are not easily biodegraded, as listed in Environment Canada (2009b): (1) terminal isopropyl groups attached to a non-cyclic chemical, and (2) a highly branched structure. Therefore, considering the model results, the empirical data for the closest analogue, and structural features, there is reliable evidence to suggest that the ultimate biodegradation half-life of zinc BDBP is > 182 days in water. In addition, the U.S. EPA considers all of the dialkyldithiophosphate group member substances, including zinc BDBP, as “P3” (i.e., high level of persistence) in their screening level hazard characterization (US EPA 2008; Federal Register 1999).

Using an extrapolation ratio of 1:1:4 for a water:soil:sediment biodegradation half-life (Boethling et al. 1995), the ultimate degradation half-life in soil is also > 182 days and the half-life in sediments is > 365 days. This indicates that zinc BDBP is expected to be persistent in soil and sediment.

In addition, the long-range transport potential (LRTP) of zinc BDBP from its point of release to air is estimated to be negligible according to its very low partitioning to air and low persistence in this medium.

Based on the empirical and modelled data (see Tables 5a and 5b above) zinc BDBP meets the persistence criteria in water, soil and sediment (half-lives in soil and water = 182 days and half-life in sediment = 365 days), but does not meet the criteria for air (half-life in air = 2 days) as set out in the Persistence and Bioaccumulation Regulations (Canada 2000).

Potential for Bioaccumulation

Since no experimental bioaccumulation factor (BAF) and/or bioconcentration factor (BCF) data for zinc BDBP were available, a predictive approach was applied using available BAF and BCF models as shown in Table 6 below. According to the Persistence and Bioaccumulation Regulations (Canada 2000) a substance is bioaccumulative if its BCF or BAF is > 5000; however, measures of BAF are the preferred metric for assessing bioaccumulation potential of substances. This is because BCF may not adequately account for the bioaccumulation potential of substances via the diet, which predominates for substances with log K_ow> ~4.0 (Arnot and Gobas 2003). Kinetic mass-balance modelling is in principle considered to provide the most reliable prediction method for determining the bioaccumulation potential because it allows for correction based on ADME (absorption, distribution, metabolism and elimination) parameters as the log K_ow of the substance is within the log K_ow domain of the model. Unfortunately results from the Arnot and Gobas model could not be used in this assessment since few of the chemicals used in its training have log K_ows above 9. The empirical log K_ow value for zinc BDBP is likely > 9 as the modelled log K_ow is 12.32 (see Table 2 above). This suggests that this chemical has low potential to bioaccumulate in the environment due to strong adsorption to organic materials and very low water solubility resulting from a high molecular weight, including many carbons. These factors favour a low bioavailability in water.

Table 6. Modelled data for bioaccumulation of zinc BDBP

The OASIS and BCFWIN modelled values in Table 6 are considered to be of acceptable reliability as some chemicals of structural comparability are contained in the training sets. The low values (7.6-32.8 L/Kg) from these models show that low bioavailability to water organisms and low dietary accumulation are likely.

The available evidence indicates that zinc BDBP is expected to have low bioaccumulation potential due to its physical and chemical properties. This conclusion is consistent with that of the U.S. EPA, which considers all of the dialkyldithiophosphate group member substances including zinc BDBP to be “B1” (i.e., low bioaccumulation potential) in their screening level hazard characterization (US EPA 2008; Federal Register 1999).

Therefore, considering the available evidence, zinc BDBP does not meet the bioaccumulation criteria (BCF, BAF = 5000) as set out in the Persistence and Bioaccumulation Regulations (Canada 2000).

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Potential to Cause Ecological Harm

Ecological Effects Assessment

A - In the Aquatic Compartment

There is experimental and modelled evidence that zinc BDBP causes harm to aquatic organisms at relatively low concentrations.

The U.S. EPA has requested that empirical data on the zinc dialkyldithiophospate category (that includes zinc BDBP) be generated in order to produce a screening-level risk assessment for this category of chemical to support its initial Risk-Based Prioritizations (RBPs) for High Production Volume (HPV) chemicals (US EPA 2008). The European Commission undertook a similar exercise where industry submitted data that were compiled in the form of IUCLID files following regulations on the Evaluation and Control of the Risks of European Existing Substances (European Commission 2000a; 2000b; 2000c; 2000d; 2000e). Seven substances of the dialkyldithiophospate category have IUCLID files, including zinc BDBP. The aquatic toxicity information, related to the dialkyditiohosphates, from these two sources was compiled and a Species Sensitivity Distribution (SSD) was then generated with the datasets (see Figure 1, below). The intent is to use the 5th percentile of the SSD as the critical toxicity value (CTV). The lowest acute aquatic toxicity value was identified for each of the 8 species included in the dataset (see Table 7, below). The group included two marine invertebrate species (Crassostrea virginica and Mysidopsis bahia). They were included in the SSD due to the limited number of species. The assumption made is that the SSD reflects the most toxic zinc dialkyldithiophosphate category member substances, which are shorter chain/lower molecular weight ones. The software SSD Master v2.0 (SSD Master 2008) was used to plot the SSD. Several cumulative distribution functions (CDFs) (normal, logistic, Gompertz, Weibull and Fisher-Tippett) were fit to the data using regression methods. Model fit was assessed using statistical and graphical techniques. The best model was selected based on consideration of goodness-of-fit and model feasibility. Model assumptions were verified graphically and with statistical tests. The Normal model provided the best fit of the models tested (Anderson-Darling Statistic (A²) = 0.316) and the 5th percentile of the SSD plot is 0.017 mg/L with lower and upper confidence limits of 0.05 and 0.057 mg/L, respectively (Figure 1). This is selected as the short-term CTV. As no chronic data could be found in the dataset, a long-term SSD could not be drawn. Therefore, an application factor of 10 was used to convert the short-term CTV to a long-term (chronic) predicted no effect concentration (PNEC). As a result, the long-term (chronic) PNEC is calculated to be 0.017 mg/L.

Robust Study Summaries (RSS) could not be generated to assess the reliability of the studies, given the lack of information in the IUCLID sources. However, an RSS was created for the lowest value of the closest analogue of zinc BDBP (CAS RN 84605-29-8) (US EPA 2008). The LL₅₀ (loading rate causing 50% mortality) for rainbow trout (Oncorhynchus mykiss) was 4.5 mg/L (see RSS in Appendix 1). The reliability of the study was satisfactory. An application factor (AF) of 100 was applied to the LL₅₀ to account for interspecies and intraspecies variability in sensitivity and to estimate a long-term no-effects concentration from a short-term LL₅₀. Application of the AF to the LL₅₀ results in a PNEC value of 0.045 mg/L.  

The PNEC calculated from the SSD (0.017 mg/L) was used preferably over the single deterministic value from the analogue loading rate study because it is likely to more accurately reflect the natural variability of responses to the dialkyldithiophosphate category member substances. The SSD value of 0.017 mg/L is also below the predicted water solubility of zinc BDBP and the experimental water solubility of its analogues.

Table 7. Empirical data for aquatic toxicity of dialkyldithiophospate category member substances used in the SSD

Figure 1. Species Sensitivity Distribution for the acute toxicity of the dialkydithiophosphate category

B - In Other Environmental Compartments

No ecological effects studies were found for this compound in media other than water. Effect levels have not been estimated for soil or sediment.

Ecological Exposure Assessment

No data concerning concentrations of this substance in water in Canada have been identified; therefore environmental concentrations are estimated from available information, including substance quantities, estimated release rates, and information on the potential size of receiving water bodies. 

Industrial Release

As zinc BDBP is used industrially and is expected to be released to water, a conservative industrial release scenario is used to estimate the aquatic concentration of the substance (Environment Canada 2009d). The scenario is made conservative by assuming that the total quantity of the substance used by Canadian industry in the reporting range (100 000 kg) is used by one single industrial facility at a small, hypothetical site. Considering that a proportion of the total quantity of the substance was not subject to industrial type releases (importation of consumer products), it was more appropriate to use 100 000 kg rather than 1 000 000 kg. The loss to sewers is at 0.31% of the total quantity resulting from mainly container handling and blending. The scenario also assumes that the release occurs 250 days per year, typical for small and medium-sized facilities, and is sent to a local primary sewage treatment plant (STP) with a 57.3% removal rate for the substance based on AS treat 1.0 (Environment Canada 2009d). In Canada , the receiving water at such a small site normally has a 10-fold dilution capacity for the STP effluent, which equals 3456 m³ per day for the size of the site. Based on the above assumptions, an aquatic concentration of 0.0153 mg/L is estimated for a small generic site (Environment Canada 2009e).

Consumer Release

As zinc BDBP is found in consumer products and is reported to be released to water, Mega Flush, Environment Canada’s spreadsheet tool for estimating down-the-drain releases from consumer uses was employed to estimate the potential substance concentration in multiple water bodies receiving sewage treatment plant effluents to which consumer products containing the substance may have been released (Environment Canada 2009f). The spreadsheet tool is designed to provide these estimates based on conservative assumptions regarding the amount of substance used and released by consumers.

By default, primary and secondary STP removal rates are conservatively assumed to be 0%.  Losses from use are assumed to be of 2.5%, consumer use of the substance to be over 365 days/year, and the flow rate at all sites to be low – i.e., equal to the tenth percentile of annual flows. These estimates are made for approximately 1000 release sites across Canada , which account for most of the major STPs in the country.

The equation and inputs used to calculate the predicted environmental concentration (PEC) of zinc BDBP in the receiving water bodies are described in Environment Canada (2009g). A scenario was run assuming a total consumer use quantity of 1 000 000 kg/year, which is a worst-case condition since it is the highest possible imported quantity in the reporting range (Environment Canada 2009g).  In addition the proportion of the total mass that is lost to sewers was set at 2.5% based on the Mass Flow Tool which estimated potential releases to soil and sewers during the life cycle of the substance (leaks, spills during use, improper disposal). Default values were used for other parameters.

Using this scenario, the tool estimates that the PEC in the receiving water bodies ranges from 0.00098 to 0.038 mg/L.

Characterization of Ecological Risk

The approach taken in this ecological screening assessment was to examine various supporting information and develop conclusions based on a weight-of-evidence approach and using precaution as required under CEPA 1999. Lines of evidence considered include results from a conservative risk quotient calculation, as well as information on persistence, bioaccumulation, inherent toxicity, sources and fate of the substance and its analogues.

Zinc BDBP is expected to be persistent in water, soil and sediment; it is also expected to have a low bioaccumulation potential. The high importation volumes of zinc BDBP into Canada , along with information on its uses, indicate moderate potential for releases to the Canadian environment. Once released to the environment, it will be found mainly in soil and sediments. It has also been demonstrated to have a low to moderate potential for toxicity to aquatic organisms.

A risk quotient analysis, integrating conservative estimates of exposure with toxicity information, was performed for the aquatic medium to determine whether there is potential for ecological harm in Canada . The conservative industrial scenario (the total quantity of the substance used by Canadian industry in the reporting range) presented above yielded a predicted environmental concentration (PEC) of 0.0153 mg/L (Environment Canada 2009e). A long-term (chronic) predicted no-effect concentration (PNEC) was derived using the 5th percentile short-term SSD value of 0.17 mg/L, and dividing this value by an assessment factor of 10 to give a value of 0.017 mg/L. The resulting risk quotient (PEC/PNEC) = 0.9. Given the conservatism in both the PEC and PNEC, this result indicates that harm to pelagic aquatic organisms is unlikely. Using a similar PEC/PNEC approach, the consumer release scenario tool predicted that conservative PECs for zinc BDBP do not exceed the PNEC in most (99.7%) of the water bodies receiving wastewater across Canada under low (10th percentile) flow conditions (Environment Canada 2009g) and assuming no STP removal. The highest PEC/PNEC ratio was 2.2.

As noted previously, when zinc BDBP is released to a water body, it partitions into suspended particulate matter and to bottom sediments, where sediment-dwelling organisms would be exposed to the substance. Because no environmental monitoring data or toxicity data specific to sediment-dwelling organisms are available, a risk quotient based on exposure in sediment pore water may be calculated based on the aquatic compartment PEC and PNEC values presented above and used for sediment risk characterization. In the calculation, bottom sediment and its pore water are assumed to be in equilibrium with the overlying water, and benthic and pelagic organisms are assumed to have similar sensitivities to the substance. Therefore the PEC and PNEC for sediment pore water is considered to be the same as for the aquatic compartment. This equilibrium approach would therefore result in risk quotients for the sediment compartment that are the same as for the aquatic compartment, i.e., almost all would be less than 1.

This information indicates that zinc BDBP does not have the potential to cause ecological harm in Canada .

Uncertainties in Evaluation of Ecological Risk

Although no information is available on the quantity of zinc BDBP that is imported in manufactured items or consumer products, it is expected that the quantities of zinc BDBP released to water would not be significantly greater than those estimated here. This is because a bounding high-end value of 1 000 000 kg was assumed to represent the mass in Canadian commerce for the consumer release scenario calculations. It is also recognized that potential releases from waste disposal sites could be possible and contribute to overall environmental concentration. However, available information is currently not sufficient to derive quantitative estimates for these releases.

Also, regarding ecotoxicity, based on the predicted partitioning behaviour of this chemical, the significance of soil and sediment as important media of exposure is not addressed by the effects data available. Indeed, the only effects data identified apply primarily to pelagic aquatic exposures, although the water column is likely not the medium of primary concern based on partitioning estimates.

The Species Sensitivity Distribution presented in this screening assessment does not meet the requirements of a type A guideline (CCME 2007) but was used since the PNEC derived from it is lower than the PNEC based on the lowest acceptable toxicity value and thus represents a more conservative scenario based on the whole dialkyldithiophosphate category.

Finally, there is uncertainty in concluding outside a moiety-based assessment on individual substances that can contribute to the total release of bioavailable zinc to the environment. The conclusion reached in this assessment, that zinc BDBP does not dissociate significantly (releasing zinc) in the environment and has a low potential to cause ecological harm in Canada , does not preclude the possible inclusion of this substance in a future moiety-based assessment of zinc-containing compounds.

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Potential to Cause Harm to Human Health

Exposure Assessment

Environmental Media

There were no data identified for zinc BDBP in environmental media, regardless of location. In the absence of release data from publicly available inventories and since in responses to a notice issued under section 71 of CEPA 1999, no releases were reported, as a conservative approach, environmental concentrations were estimated using the loss percentages predicted by the Mass Flow Tool by Environment Canada (see Table 3) (Environment Canada 2009c). The percentages represent losses of a substance at different stages of the life cycle and were applied to the total quantity of zinc BDBP in Canadian commerce in 2006.

The total quantity in commerce was conservatively assumed to be the maximum of the import range for 2006, namely 1 000 000 kg (Environment Canada 2009a). The loss quantities are estimated as 19 000 kg to water through wastewater, 11 000 kg to soil through leaching from landfill and 9000 kg to paved/non-paved surfaces. These loss quantities to water and soil are considered as overestimates, as explained in the Releases to the Environment section.

The estimated losses were used in ChemCAN, a Canada-specific environmental exposure model, to estimate concentrations in various environmental media (ChemCAN 2003). The predicted concentrations are presented in Appendix II. This model differs from the point-source models used in the ecological assessment section of the document in that it is a regional far-field Level III fugacity model that is used to estimate average concentrations in various media to inform human exposure estimates. The estimated environmental concentrations were used as surrogates for measured data in deriving intake estimates. The estimated concentration in ambient air was used as a surrogate for indoor air data. In addition, the estimated concentration in surface water was used as a surrogate for drinking water. The intake estimates for each medium, in addition to total intake for each age group, are presented in Appendix III. The maximum total intake estimate was in the order of magnitude of 10^-3 µg/kg-bw, which indicates that environmental exposure is considered negligible in comparison to potential exposure to zinc BDBP in consumer products.

Consumer Products

In order to estimate exposure to zinc BDBP for consumers, dermal exposure for a do-it-yourself (DIY) motor oil change was considered a worst-case source of exposure in finished oils due to the high likelihood of hand exposure during the change. Motor oils are agents that serve anti-wear and cooling functions for running equipment parts and must be periodically replaced, either at the dealer, repair garage or by the consumer.

A DIY motor oil change involves draining used oil, replacing the filter and pouring new oil into the engine crankcase using a funnel (eHow 2009). In an empirical study of zinc dithiophosphate levels in used motor oil, depletion of levels occurred at a roughly linear rate in two used oil samples tested at regular intervals of driving time (Yamaguchi et al. 2002). Assuming that some older cars require an oil change approximately every 4800 km, a vehicle traveling an average speed of 50 km/h would require an oil change every 96 hours (eHow 2009). At 96 hours of driving, approximately 40% of the total zinc BDBP would be depleted (Yamaguchi et al. 2002). Therefore, the dermal load of zinc BDBP after possible hand spillage during the draining phase of a motor oil change would be less than for exposure to new oil. However, the finger of the consumer is often used to lubricate the filter using new motor oil. In addition, the pouring of new motor oil into the engine crankcase presents another opportunity for potential hand spillage. A worst-case internal acute dose for dermal exposure to motor oil during an oil change of 0.858 mg/kg-bw per event was determined. The dermal scenario is presented in Appendix IV.

Health Effects Assessment

Only limited toxicological data are available for zinc BDBP. The acute toxicity is low, with an LD₅₀ determined to be between 2000 and 5000 mg/kg-bw by gavage in rats (Anonymous 1986). New Zealand White rabbits dermally exposed to 0.8 mL/kg (converted to 884 mg/kg-bw/day ^[3]) or 1.6 ml/kg for three weeks showed irritation, body weight loss and elevated white blood cell count at both high and low doses. Effects in the high-dose groups included decreased mean testes weights, testes to body weights ratios and testes to brain weight ratios and decreased spermatogenic activity. A no-observed-effect level (NOEL) could not be established (Anonymous 1979).

The outputs of predictive models were also considered using four different models, Derek, TopKat, CaseTox and Leadscope Model Applier, of which the predictions for carcinogenicity, genotoxicity, developmental toxicity, and reproductive toxicity were predominately negative (DEREK 2008; TOPKAT 2004; CASETOX 2008; Leadscope 2009).

The U.S. EPA has conducted a screening level risk characterization of the zinc dialkyldithiophosphates which included zinc BDBP (US EPA 2008). The hazard characterization for zinc BDBP indicates that the acute oral toxicity is low based on measured data, and the acute dermal toxicity is low based on a read-across approach, which compared zinc BDBP to analogue substances. A no-observed-adverse-effect level (NOAEL) of 10 mg/kg-bw/day and a lowest-observed-adverse-effect level (LOAEL) of 50 mg/kg-bw/day was established for repeat-dose oral toxicity based on read-across data from one study of an analogue substance, which showed moderate systemic toxicity. The reproductive/developmental endpoint was filled, also using read-across data from a single oral study in which a NOAEL of 30 mg/kg-bw/day and a LOAEL of 100 mg/kg-bw/day were established for reproductive, developmental and systemic effects. Read-across data were negative for mutagenicity in bacterial cells, but showed a positive response in mammalian cells, and in vivo did not induce chromosome aberrations.

Characterization of Risk to Human Health

The potential for exposure of the general population to zinc BDBP from environmental media is expected to be negligible. However, there is potential for dermal exposure from the use of consumer products (additive in motor oil).

A comparison between the short-term dermal lowest-observed-effect level (LOEL) of 884 mg/kg-bw/day in New Zealand White rabbits and the estimated maximum total daily intake from all routes of environmental exposures in the order of magnitude of 10^-3 µg/kg-bw/day results in a margin of exposure (MOE) in the order of magnitude of 10⁸. This same short-term dermal LOEL of 884 mg/kg-bw/day and dermal exposure for consumer products (additive in motor oil) of 0.858 mg/kg-bw result in an MOE of 1030. Based on the information available, these margins are considered adequate to account for uncertainties in the database, in light of the conservative nature of the estimates of exposure and critical effect level.

Uncertainties in Evaluation of Risk to Human Health

Confidence in the environmental exposure estimates is moderate. Data in the literature were not identified for concentrations in environmental media. However, since no releases were reported in response to a notice issued under section 71 of CEPA 1999, in conjunction with the conservative use of loss quantities predicted by the Mass Flow Tool to represent worst-case release estimates, it is unlikely that the intake values are underestimates. Confidence in the consumer product exposure estimate is moderate. While end products in current use in Canada are considered to have been comprehensively captured in the responses to a notice issued under section 71 of CEPA 1999, the duration of dermal exposure and the skin surface area exposed were based on professional judgment in the do-it-yourself motor oil scenario.

The 3-week dermal study did not establish a NOEL. However, the effects observed at the LOEL were considered minor. Due to the limited data available for zinc BDBP, the confidence in the toxicological dataset is considered to be low. However, the available empirical data and information from predictive models are not suggestive of high hazard.

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Conclusion

Based on the information presented in this screening assessment, it is concluded that zinc BDBP is not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends. Zinc BDBP meets the criteria for persistence but not for bioaccumulation potential as set out in the Persistence and Bioaccumulation Regulations(Canada 2000).

It is also concluded that zinc BDBP is not entering the environment in a quantity or concentration or under conditions that constitute or may constitute a danger in Canada to human life or health.

It is therefore concluded that zinc BDBP does not meet any of the criteria in section 64 of CEPA 1999.  

This substance will be considered for inclusion in the Domestic Substances List inventory update initiative. In addition and where relevant, research and monitoring will support verification of assumptions used during the screening assessment.

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Appendix 1: Robust Study Summary

Robust Study Summaries Form and Instructions: Aquatic iT

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Appendix 2: Estimated concentrations of zinc BDBP in environmental media using ChemCAN version 6.00 (ChemCAN 2003)¹

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Appendix 3: Estimates of total and media-specific daily intakes of zinc BDBP for various age groups

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Appendix 4: Dermal exposure estimate for a do-it-yourself motor oil change

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Appendix 5: Summary of (Q)SAR Results for Zinc BDBP

(Q)SAR Predictions pm Carcinogenicity

 

(Q)SAR Predictions on Genotoxicity

 

 

(Q)SAR Predictions on Developmental Toxicity

Model Applier

 

Multicase Casetox

 

(Q)SAR Predictions on Reproductive Toxicity

Model Applier

 

Multicase CaseTox

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Appendix 6: PBT Model Inputs Summary Table

Footnotes

^[1] A determination of whether one or more of the criteria of section 64 are met is based upon an assessment of potential risks to the environment and/or to human health associated with exposures in the general environment. For humans, this includes, but is not limited to, exposures from ambient and indoor air, drinking water, foodstuffs, and the use of consumer products. A conclusion under CEPA 1999 on the substances in the Chemicals Management Plan (CMP) Challenge Batches 1-12 is not relevant to, nor does it preclude, an assessment against the hazard criteria specified in the Controlled Products Regulations, which is part of regulatory framework for the Workplace Hazardous Materials Information System [WHMIS] for products intended for workplace use.
^[2] For example, an analogue CAS RN 4259-15-8, Phosphorodithioic acid, O,O-bis(2-ethylhexyl) ester, zinc salt shows no effects at saturation to rainbow trout (Oncorhynchus mykiss) and at loading rates up to 100 mg/L (US EPA 2008).
^[3] Conversion of 0.8 mL/kg to mg/kg
= (density of zinc BDBP)(volume conversion factor)(volume of substance/kg body weight)
= (1.105 g/cm³)(1 cm³/mL)(0.8 mL/kg-bw)
= 0.884 g/kg-bw
= 884 mg/kg-bw

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