Bioavailability of Bound Pesticide Residues and Potential Toxicologic Consequences

Abstract

Conclusions

The use of ¹⁴C-labeled pesticides has made us aware of the existence of bound residues in edible tissue and plants. These residues would escape detection by the conventional analytical methods and would result in an underestimation of the edible tissue or plant burden of total pesticide residues. The methodology for the analysis of bound pesticide residues is still in the developmental stage. The total ¹⁴C-bound residues in tissues and plants are usually estimated by combustion of the extracted material to yield ¹⁴CO₂. The high temperature distillation technique and supercritical methanol may provide a possible means for the chemical identification of bound residues. However, the application of these techniques to bound residue analysis of other pesticides has not been fully explored.

A major portion of bound pesticide residues in plant tissues may be associated with lignin. Thus, lignin formation in plants may serve as a system for plants to store pesticide residues by incorporating them into insoluble lignin. The feeding of plant materials containing ¹⁴C-bound residues to monogastric animals indicates that these residues may be considered to be of little toxicological concern. However, recent studies have shown that even lignin-bound pesticide residues can be bioavailable to a great extent and may possess ecotoxicological significance (12). The binding of pesticide residues in edible tissues of meat also appears to yield fractions of residues that are not readily bioavailable. This need not necessarily be equated with safety, as the minimal levels for toxicity are not known. In addition, these small amounts of pesticide could be cumulative and toxic over time.

Whether bound pesticide residues are of any environmental significance will remain a matter of conjecture until more data are available. However, judging from the limited available information. it appears that bound residues may not present any problem as long as such residues do not accumulate in significant amounts. It is recommended that more coordinated research be undertaken for a better assessment of this complex problem.