殺菌剤グアザチンの環境中における動態

抄録

The environmental fate of the fungicide guazatine-triacetate (TA) was extensively investigated in view of safety. When applied to dwarf apple trees under laboratory conditions, ¹⁴C-guazatine-TA stayed on the leaves and fruit for a long time because of its low permeability, although an appreciable amount of guazatine was photolysed on the plant surface. The fungicide that had penetrated into apple tissues was resistant against plant metabolism, and thus the large amount persisted in an unaltered form on/in the apple tissues. In outdoor studies, however, a major part of guazatine deposit was washed out of dwarf apple trees probably due to mechanical dislodgement by the rain. This indicates that in an actual field guazatine sprayed on apple trees is mostly transferred to soil. In soil, guazatine was rapidly and strongly adsorbed to a soil inorganic fraction, became resistant to microbial degradation both under upland and flooded conditions, and persisted in soil for a long time in an unaltered form. On the other hand, guazatine soil residues were unavailable to soybean and rice plants. This suggests that human uptake of guazatine from soil residues in rotational crop fields may be negligible. Thus, guazatine residues taken into humans and animals are mostly attributable to the residues in crops to which guazatine was directly sprayed. However, more than half of ¹⁴C-residues in apple fruit was washed out with 0.1% detergent solution, which suggest that considerable amounts of guazatine crop residues would be reduced through processing. When guazatine-TA was orally administered to male rats, the bioavailability of guazatine was extremely low, while the tissue retention of absorbed guazatine was considerably high. The primary target organ for ¹⁴C-retention was the kidney, in which the principal residue was mono-deamidinated guazatine. Deamidination was the primary metabolic route of guazatine in rats, although principal urinary metabolites have yet to be identified. The average amount of guazatine remaining in the body at a steady state during repeated uptakes was calculated to be only 0.34-0.56 times the daily uptake level. Our overall studies on the environmental fate of guazatine found that in terms of safety, adverse effects of guazatine on non-target species (including man) would be small.