Table 3 (Cont.) 



This is an example toxicity profile and is not intended to be comprehensive. 



Mercury may occur in its elemental form, as inorganic salts, or as organic complexes. 

 Consequently, the chemical and toxicological properties vary tremendously depending 

 on the degree of complexation or metal speciation. 



Q 



Physical-chemical properties and toxicity vaiy according to the degree of chlorine 

 substitution, the number of adjacent unsubstituted carbons and steric configuration. 



Bioconcentration Factors are the ratio of a chemical concentration in tissues of 

 marine or estuarine organisms and the concentration in water to which the organism 

 is exposed (Tetra Tech 1985a). 



N/A = not applicable. 

 ^ U.S. EPA (1980a,b, 1986f; lARC 1978). 



° For mercury (II) choride via oral route of exposure (Tatken and Lewis 1983). 

 Relevance to consumption of mercuiy (primarily methylated) in Tish is questionable. 

 ^ Clarkson et al. (1973). 



Information in a toxicity profile is used to support the weight of 

 evidence classification for the likelihood of a chemical causing a given 

 health effect. The endpoints considered should include noncar- 

 cinogenic as well as carcinogenic effects. EPA has developed a weight- 

 of-evidence classification scheme which indicates the state of 

 knowledge on the carcinogenicity of chemicals (U.S. EPA 1986a, 

 1987a). It includes the following categories: 



• Group A - Human Carcinogen: This group is used only when 

 there is sufficient evidence from epidemiologic studies to sup- 

 port a causal association between exposure to the agent and 

 cancer. 



• Group B - Probable Human Carcinogen: This group includes 

 agents for which the weight of evidence of human carcinogeni- 

 city based on epidemiologic studies is "limited." It also includes 

 agents for which the weight of evidence of carcinogenicity 

 based on animjil studies is "sufficient." The group is divided 

 into two subgroups. Usually, Group Bl is reserved for agents 

 for which there is limited evidence of carcinogenicity from 

 epidemiologic studies. It is reasonable, for practical purposes, 

 to regard an agent for which there is "sufficient" evidence of 

 carcinogenicity in animals as presenting a carcinogenic risk to 

 humans. Therefore, agents for which there is "sufficient" 

 evidence from animal studies and for which there is "inade- 

 quate" evidence or "no data" from epidemiologic studies would 

 usually be categorized under Group B2. 



• Group C - Possible Human Carcinogen: This group is used 

 for agents with limited evidence of carcinogenicity in animals 

 in the absence of data on humans. It includes a wide variety of 

 evidence: e.g., (a) a malignant tumor response in a single, 

 well-conducted experiment that does not meet conditions for 

 sufficient evidence; (b) tumor responses of marginal statistical 

 significance in studies having inadequate design or reporting; 



(c) benign but not malignant tumors with an agent showing no 

 response in a variety of short-term tests for mutagenicity; and 



(d) response of marginal statistical significance in a tissue 

 known to have a high or variable background rate. 



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