Leachability and potential ecotoxic impact of trifluralin-impregnated mulch.

The leachability, potential ecotoxicity, and photolysis of trifluralin-impregnated mulch, a popular retail consumer gardening product, were investigated under environmentally realistic conditions. Leachability of trifluralin from impregnated mulch was low (< 1% of total extractable compound) and in the range of reported values for agricultural soils. No trifluralin transformation products were detected in mulch leachate. Yeast-based estrogenicity and androgenicity screens indicated that aqueous trifluralin is not estrogenic but is moderately androgenic at concentrations ~ 1e - 5 M. Impregnated mulch leachate was not hormonally active, even at undiluted concentrations, but it did exert nonspecific toxicity at dilutions of ~ 1:10. Photolysis of trifluralin was investigated in acetonitrile and water and on mulch surfaces. Degradation on mulch surfaces was diffusion-limited; it was ~ 17 times slower than in aqueous solution, but faster than has been reported on kaolinite. An array of trifluralin transformation products was identified, but in no case did they exceed 10% of the parent compound. Using industry-recommended application guidelines, it is estimated that as much as 1400 μg/m2 of trifluralin may leach from impregnated mulch upon the first rainfall. However, provided that consumers are aware that such mulch products contain trifluralin and are properly educated about its use, the potential for direct ecotoxic impact is likely to be small.