Adaptation of biomixtures for carbofuran degradation in on-farm biopurification systems in tropical regions.

A biomixture constitutes the active core of the on-farm biopurification systems, employed for the detoxification of pesticide-containing wastewaters. As biomixtures should be prepared considering the available local materials, the present work aimed to evaluate the performance of ten different biomixtures elaborated with by-products from local farming, in the degradation of the insecticide/nematicide carbofuran (CFN), in order to identify suitable autochthonous biomixtures to be used in the tropics. Five different lignocellulosic materials mixed with either compost or peat and soil were employed in the preparation of the biomixtures. The comprehensive evaluation of the biomixtures included removal of the parent compound, formation of transformation products, mineralization of radiolabeled CFN, and determination of the residual toxicity of the process. Detoxification capacity of the matrices was high, and compost-based biomixtures showed better performance than peat-based biomixtures. CFN removal over 98.5% was achieved within 16 days (eight out of ten biomixtures), with half-lives below 5 days in most of the cases. 3-Hydroxycarbofuran and 3-ketocarbofuran were found as transformation products at very low concentrations suggesting their further degradation. Mineralization of CFN was also achieved after 64 days (2.9 to 15.1%); several biomixtures presented higher mineralization than the soil itself. Acute toxicity determinations with Daphnia magna revealed a marked detoxification in the matrices at the end of the process; low residual toxicity was observed only in two of the peat-based biomixtures. Overall best efficiency was achieved with the biomixture composed of coconut fiber-compost-soil; however, results suggest that in the case of unavailability of coconut fiber, other biomixtures may be employed with similar performance.