Adaptation of biomixtures for the accelerated degradation of carbofuran in a tropical environment

One of the main causes of agroindustrial origen contamination is the spillage and disposal of pesticides, especially during the loading, mixing or cleaning of agricultural spraying equipments. Thus, appropriate management and treatment of these chemicals are necessary practices. One improvement in the handling of organic pollutants is the use of biopurification systems (biobeds), simple and cheap degradation systems where the pesticides are biologically degraded at accelerated rates (Castillo et al., 2008). However, design of biobeds or other biodegradation systems is dependent on regional characteristics, particularly climatic conditions and the materials/residues available for their construction, particularly the components of the biomixture, active core of the biobed (Karanasios et al., 2012). The present work aimed at screening the efficiency of several biomixtures made with waste materials from Costa Rican agricultural industry to degrade the insectice/nematicide carbofuran, in terms of removal of degradation and reduction in toxicity. A lignocellulosic substrate (rice husk, wood chips, coconut fiber, sugarcane bagasse or newspaper print), and a humic-rich material (peat or garden compost) were mixed with soil pre-exposed to carbofuran (CBF), in order to obtain ten different biomixtures. After spiking with 50 mg/kg CBF, the efficiency of the biomixture was evaluated through a multi-component approach that included: monitoring of CBF removal and production of CBF transformation products (3-hydroxycarbofuran and 3-ketocarbofuran), mineralization of radioisotopically labeled carbofuran (14C-CBF) and changes in the toxicity of the matrix after the treatment (Daphnia magna acute immobilization test). Estimated half-lives of CBF in the biomixtures ranged from 2.5 d to 10.3 d, with six out of ten mixtures showing values below 5 d. After 16 d, removal >98.5% was achieved for eight biomixtures. The best performance was exhibited by the biomixture composed of coconut fiber-compost-soil (FCS), with a half-life of 2.5 d and 79.6% elimination in 4 d. Transformation products were detected in every case at concentrations below quantification limit. Mineralization of CBF was monitored over a 63 d period. Highest mineralization rates were achieved for the mixtures composed of FCS, bagasse-compost-soil (BCS) and newspaper-peat-soil (PTS), in every case above the mineralization rate obtained in solely the pre-exposed soil (>12%). Toxicity of the biomixtures was determined after the treatment period. Initial toxicity of the matrix (after spiking the CBF solution) that was as high as 200 toxicity units (TU), was reduced to