Undesirable substances occur in foods for human consumption as inherent natural constituents in the food plants or as contaminant through their presence in the environment, through fungal contamination or through preservation and preparation processes. The risk assessment process for any of these substances consists of several steps including hazard identification, hazard characterisation, exposure assessment and risk characterisation. Particularly exposure assessment has recently been refined based on real consumption values (concise European consumption data base) and the concept of defining reference points in the assessment of toxic effects followed by the calculation of the margin of exposure. Recently, the CONTAM Panel of European Food Safety Authority (EFSA) has also evaluated more than 30 individual substances that are considered as undesirable contaminants of animal feeds. These included geological contaminants such as heavy metals, environmental pollutants such as persistent polyhalogenated hydrocarbons, natural toxins, such as mycotoxins and toxic plant secondary metabolites, as well as botanical impurities that only accidentally occur in animal feeds.
Focussing first on animal health assessment and taking natural toxins as an example, the current review aims to describe the different variables that determine the species-specific sensitivity of animals to feed contaminants. Hazard identification and exposure assessment needed to take into account the geographic and seasonal variability of feed contamination, the technical stability of contaminants in feed materials, feed composition and feeding regimes for different age groups under the conditions of modern agricultural practice. During the process of evaluation is became apparent that the large variation in diet composition even within one animal category, as well as the lack of comparable analytical data (for many of the natural contaminants no validated methods are available) were major obstacles in hazard identification and exposure assessment. Adverse health effects in animals include anti-nutritive effects, specific (organ-) toxicity, reproductive and behavioural effects, which clearly differ from the acute toxicity that is documented in the literature referring to accidental intoxications. Moreover, in many of the published reports related to target animal toxicity the actual exposure level is not stated, hindering a dose-response assessment. There is certainly a need for professional toxicological investigations in target animals to establish robust tolerance levels for certain frequently occurring natural contaminants.
The assessment of consumer's risks resulting from residual amounts of undesirable substances in animal derived products is preceded by an analysis of kinetic data in target animal species to identify biotransformation and tissue disposition. The evaluation of substance-specific (toxico)kinetic parameters needs to be supported by food consumption data to estimate the actual exposure level of the human population that forms the basis of a hazard characterization. In most cases animals detoxify and/or excrete xenobiotics rapidly and the level of residues in edible tissue remains low, contributing only to a limited extent to human exposure. However, a number of lipophilic compounds that accumulate in animal tissues or in aquatic food chains require continuous attention.
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J. Fink-Gremmels
Utrecht University , Faculty of Veterinary Medicine, Div. Veterinary Pharmacology and Toxicology, The Netherlands |
