Follow-up to ecological risk assessment of organotin substances on domestic substances list: synopsis


Synopsis

There are 109 organotin substances on Canada’s Domestic Substances List (DSL), 104 of which belong to nine subcategories of organotins, as outlined in Table 1. Tetrabutyltins are not on the DSL, but a tetrabutyltin has been evaluated by the New Substances program and is suspected to be toxic to the environment. Tetrabutyltins can also degrade to tributyltins in the environment and are therefore also addressed in this report. The remaining five organotin substances on the DSL do not belong to these subcategories, and these five substances are not addressed.

Table 1: Organotin Subcategories: Number of Organotin Substances on the DSL
  Methyltin Butyltin Octyltin Phenyltin
Mono- 13 18 2 0
Di- 15 38 8 0
Tri- 0 8 0 1
Tetra- 0 0 0 1

Approximately 70% of the total annual world production of non-pesticidal organotin compounds is used in PVC stabilizers. Mono- and dialkyltins (i.e. methyl-, butyl- and octyltins) are used mainly as polyvinyl chloride (PVC) stabilizers. Dioctyltins are generally used as additives for PVC food packaging products. Some mono- and dialkyltins (e.g. butyltin trichloride and dimethyltin dichloride) are also used in depositing clear, durable tin oxide coatings on reusable glass bottles. Certain dialkyltins are used as catalysts in producing various polymers and esters. Internationally, dialkyltins are also used as stabilizers for lubricating oils, hydrogen peroxide and polyolefins.

It is believed that almost all of the intentional use of tributyltins in Canada is related to its pesticidal properties, which are regulated under the Pest Control Products Act (PCPA). Action has already been taken on tributyltin pesticides with the greatest exposure to the environment. The use of tributyltins in antifouling paint for use on ship hulls has been prohibited in Canada since January 1, 2003 under the PCPA. As of March 1, 2009, two tributyltin active ingredients were registered under the PCPA and are found in six end-use products. The Pest Management Regulatory Agency of Health Canada intends to re-evaluate the remaining uses of tributyltin by 2009-2010, to determine if their use continues to be acceptable under today’s standards for health and environmental protection.

Trialkyltins occur as contaminants in other commercial organotin products. It has been reported that tributyltins can be impurities at concentrations up to about 20% in tetrabutyltins imported for use in the synthesis of organotin stabilizers. Tributyltins are also present at lower concentrations (up to about 0.5%) in commercial dibutyltin formulations.

Tetraalkyltins are believed to be used in Canada only as intermediates in the synthesis of other organotin substances.

Tetraphenyltin and one triphenyltin substance, fluorotriphenyltin, are listed on the DSL. However, based on information provided by industrial suppliers of organotin substances, it is believed that fluorotriphenyltin and tetraphenyltin are not currently in use in Canada.

Methyltin compounds may be present in the environment both as a result of natural methylation of inorganic tin and from industrial uses. Other types of organotins are not formed by natural processes in the environment.

In Canada, the largest environmental releases of non-pesticidal organotins are expected to occur as a result of loss of liquid residues from shipping containers, with smaller releases occurring from storage tanks and transfer lines during processes associated with formulation and manufacturing. It is estimated that up to 0.4 kg of organotin stabilizers per day could be released into water from a facility in the absence of appropriate stewardship practices. In recent years, facilities using organotin stabilizers have adopted product stewardship practices that have led to a decrease in the potential release of organotins. Releases from these facilities are estimated to be less than 0.0016 kg/day. Environmental concentrations resulting from these releases would not be expected to harm aquatic organisms.

An Environmental Performance Agreement (EPA) was entered into between Environment Canada, the Vinyl Council of Canada and the Tin Stabilizers Association to provide the continued implementation of effective stewardship practices for organotin stabilizers. The final EPA was signed on March 10th 2008.

Tributyltins and triphenyltins meet the criterion for persistence in sediments and the criteria for bioaccumulation set out in the Persistence and Bioaccumulation Regulations, a regulation made under the authority of the Canadian Environmental Protection Act, 1999. These substances are not naturally occurring radionuclides or naturally occurring inorganic substances, and their presence in the environment results from human activity. In the past, tributyltin compounds have probably entered the environment mostly from their pesticidal uses in antifouling paints. However, tributyltin compounds may also enter the environment because of their presence in other butyltin products and from the environmental breakdown of tetrabutyltins. Tetrabutyltins may enter the environment during the synthesis of other butyltin substances Tributyltins have been detected in surface water and sediment throughout Canada, whereas triphenyltins have been detected in sediment samples from several sites in Canada. These substances are harmful to aquatic organisms at low concentrations. Concentrations of tributyltins at some sites in Canada are high enough to harm aquatic organisms.

Tetrabutyltins are degraded in the environment by removal of one of the alkyl groups attached to the tin atom, producing tributyltin compounds. Tetraphenyltin is expected to degrade to triphenyltin compounds in a similar manner. Furthermore, commercial formulations of tetrabutyltins contain tributyltins as by-products, and tetraphenyltin would also be expected to contain triphenyltins as by-products. As precursors to persistent and bioaccumulative compounds that have the potential to cause environmental harm, tetrabutyltins and tetraphenyltin are themselves considered to have the potential to cause harm to the environment.

Based on the available information on their potential to cause ecological harm, it is concluded that tributyltins and tetrabutyltins are entering, or may enter, 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. Therefore, it is concluded that tributyltins and tetrabutyltins meet the criterion set out in paragraph 64(a) of the Canadian Environmental Protection Act, 1999.

Based on the available data on their potential to cause ecological harm, it is concluded that monomethyltins, monobutyltins, monooctyltins, dimethyltins, dibutyltins, dioctyltins, fluorotriphenyltin and tetraphenyltin are currently 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. Therefore, it is concluded that monomethyltins, monobutyltins, monooctyltins, dimethyltins, dibutyltins, dioctyltins, fluorotriphenyltin and tetraphenyltin do not meet the criteria set out in paragraphs 64(a) or 64(b) of the Canadian Environmental Protection Act, 1999. However, given the hazardous properties of fluorotriphenyltin and tetraphenyltin, there is concern that new activities for these two substances which have not been identified or assessed could lead to the substances meeting any of the criteria set out in section 64 of the Act. It is thus recommended that these two substances be subject to the Significant New Activity provisions specified under subsection 81(3) of the Act, to ensure that any new manufacture, import or use is notified and will undergo ecological and human health risk assessments as specified in section 83 of the Act prior to being introduced into Canada.

A final follow-up report on the review of critical data on the potential effects of non-pesticidal organotin substances on humans and on the estimated exposure of humans to these substances was released publicly in May, 2003. This review concluded that non-pesticidal organotin substances were 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 this review, the Minister of the Environment and the Minister of Health concluded that non-pesticidal organotin substances did not meet the criterion set out under paragraph 64(c) of the Canadian Environmental Protection Act, 1999.

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