Fate of xenobiotics during composting

A primary concern with composting is the lack of knowledge about the fate of widely used pesticides. Also, there is increasing interest in the use of composting as a bioremediation method for soils contaminated with xenobiotics such as TNT, PCBs, chlorophenols and PAHs. We used a laboratory scale composting system to determine the extent of mineralization, incorporation into humic matter, and volatilization, during the composting of yard trimmings amended with 14 C labeled pesticides such as 2,4-D, diazinon, and pendimethalin. Our results showed that the pesticides studied have very different fates during composting. For example, 2,4-D is rapidly mineralized and transformed into high molecular weight humic compounds. Diazinon, on the other hand, is not readily mineralized, but undergoes rapid transformation to water soluble metabolites, while pendimethalin appears to be converted primarily into unextractable residues. Atrazine mineralization during composting is limited and varies with different lignocellulosic substrates. Preliminary results show that limited degradation of PCBs occurs during the composting of contaminated soils. Our results also indicate that thermophilic microbial communities are involved in the mineralization and biotransformation of xenobiotics during composting.