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A proposal has been developed by the Agricultural Chemical Safety Assessment (ACSA) Technical Committee of the ILSI Health and Environmental Sciences Institute (HESI) for an improved approach to assessing the safety of crop protection chemicals. The goal is to ensure that studies are scientifically appropriate and necessary without being redundant, and that tests emphasize toxicological endpoints and exposure durations that are relevant for risk assessment. The ACSA Systemic Toxicity Task Force proposes an approach to systemic toxicity testing as one part of the overall assessment of a compound's potential to cause adverse effects on health. The approach is designed to provide more relevant data for deriving reference doses for shorter time periods of human exposure, and includes fewer studies for deriving longer term reference doses-that is, neither a 12-month dog study nor a mouse carcinogenicity study is recommended. All available data, including toxicokinetics and metabolism data and life stages information, are taken into account. The proposed tiered testing approach has the potential to provide new risk assessment information for shorter human exposure durations while reducing the number of animals used and without compromising the sensitivity of the determination of longer term reference doses.

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Marine mussels Mytilus edulis accumulate radionuclides of cobalt, zinc, ruthenium, silver and caesium in the soft tissues hnearly over time during exposure periods up to 9 d. Radiotracer binding to shell is rapid, but variable, and is essentially complete after 1 d. The distribution between soft tissues and shell varies with each metal and exposure period, and ranges from 1 : 25 for caesium and sdver to 1 : 1 for cobalt after 9 d. Radiotracer contents of all isotopes in the mussels are lognormally distnbuted. Radionuclide contents after exposure increase with shell length and are best described by power functions of body weight. After 9 d of exposure both ruthenium and silver exhibit a typical surface-type behamour, where the metal content of the mussels is proportional to their surface area. By contrast, cobalt, zinc and caesium exhibit a metabolic-type behaviour. The effect of inherent vanabdity of the mussel population with respect to the accumulation of the radiotracers is discussed, as are implications for sampling programmes.