Screening assessment report for chlorinated naphthalenes: chapter 1

Synopsis

Pursuant to section 74 of the Canadian Environmental Protection Act, 1999 (CEPA), the Ministers of the Environment and of Health have conducted a screening assessment on chlorinated naphthalenes. "Naphthalene, chloro derivatives", Chemical Abstracts Service Registry Number 70776-03-3, was identified as meeting the categorization criteria for persistence, bioaccumulation potential and inherent toxicity to non-human organisms. "Naphthalene, chloro derivatives" is a variable chemical mixture that covers the chemical class of chlorinated naphthalenes,

Chlorinated naphthalenes 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.

Chlorinated naphthalenes (CNs) have the molecular formula C₁₀H_8-nCl_n (n = 1-8). There are 75 possible chlorinated naphthalenes in eight homologue groups, based on the number of chlorine atoms in the molecule. These homologue groups are referred to using the prefixes mono- to octa- (for example, mono-CNs, di-CNs). The number and, to a lesser extent, the positions of the chlorine atoms within the CN molecule are the key determinants of the physical and chemical properties of the CN congeners.

Key physical and chemical properties are useful when predicting the environmental fate of CNs. Water solubility, vapour pressure and Henry's law constant values tend to decrease when progressing from mono- to octa-CNs, while log K_ow, melting point and boiling point tend to increase when progressing from mono- to octa-CNs.

Sources of CNs in the environment are mainly anthropogenic. Beginning around 1910, mono- to octa-CNs were produced commercially for a variety of uses. CNs were likely never manufactured in Canada but they were imported from manufacturers in the U.S. Although CNs have not been in commercial use in Canada for more than two decades, they could be produced unintentionally as a by-product of industrial processes involving chlorine, especially in the presence of heat, such as waste incineration, cement and magnesium production, refining of metals such as aluminium, drinking water chlorination and pulp and paper production (chloralkali process). Releases resulting from some of these processes have not been well characterized. Other sources of CNs in the environment include products containing CNs deposed of in landfill sites and old industrial sites where CNs were used. There are reports of CNs being released into the atmosphere from the domestic combustion of wood. A possible non-anthropogenic (natural) source of CNs is the combustion of wood during forest fires.

Fugacity modelling is used to predict into which environmental compartments CNs will partition. CNs tend to partition mainly into air and soil when released only into the air. CNs tend to partition mainly into water and sediment when released only into the water.

CNs have been detected in the following samples in Canada: Arctic and urban air, Lake Ontario water, fish and birds from the Great Lakes and environs, Pacific killer whales, seals and whales from the Canadian Arctic, and Vancouver Island marmots. The data on environmental concentrations of CNs in Canada are limited. Much more environmental data on CNs, including from sediments and soils, have been collected in the U.S. and Europe.

Di- through octa-CNs are persistent in air. The potential for long-range transport has been estimated to be moderate for di-CNs and high for tri- through octa-CNs, indicating that some CNs may be subject to atmospheric transport to remote regions such as the Arctic. In addition, di- through octa-CNs are predicted to be persistent in water, and tri- through hepta-CNs are persistent in both sediment and soil. Based on the weight of evidence, including, in particular, measured log K_ow values for di- to octa-CNs, the measured bioconcentration values for di-to penta-CNs in fish, measured biomagnification factors for tetra- to hepta-CNs, the high dietary uptake efficiencies of hexa to octa-CNs in northern pike and the very slow elimination of hexa-CNs from rats and humans, it is concluded that di- to octa-CNs are also bioaccumulative.

The available empirical and modelled aquatic toxicity data for CNs indicate that di-, tri-, tetra- and penta-CNs may, at relatively low concentrations, be harmful to aquatic organisms (below 1 mg/L for acute tests, and 0.1 mg/L for chronic tests). Hexa-, hepta- and octa-CNs were found to cause harmful effects in mammals (particularly cattle) at doses of 0.69 mg/kg body weight per day or more.

Evidence that a substance is highly persistent and bioaccumulative--as defined in the Persistence and Bioaccumulation Regulations under the Canadian Environmental Protection Act, 1999 -- when taken together with potential for environmental release or formation and potential for toxicity in organisms, -- provides a significant indication that the substance may be entering the environment under conditions that may have harmful long-term ecological effects. Substances that are persistent remain in the environment for a long time after being released, increasing the potential magnitude and duration of exposure. Substances that have long half-lives in air and water and partition into them in significant proportions have the potential to cause widespread contamination. Releases of small amounts of bioaccumulative substances may lead to high internal concentrations in exposed organisms. Highly bioaccumulative and persistent substances are of special concern, since they may biomagnify in food webs, resulting in very high internal exposures, especially for top predators.

Based on the lines of evidence presented above, particularly the evidence for persistence, bioaccumulation and potential to cause harm at low exposure values, and taking into account the limitations of existing quantitative risk estimation methods when applied to such substances, especially ones such as CNs for which there are limited data, and recognizing that although CNs are no longer in commercial use in Canada they continue to enter the Canadian environment from unintentional production as well as through transboundary movement of air, it is concluded that di- through octa-CNs have the potential to cause environmental harm in Canada.

Therefore, it is proposed that polychorinated naphthalenes are entering the environment in quantities or concentrations, or under conditions that have or may have immediate or long-term harmful effects on the environment or its biological diversity.