Effects of long-term contamination of DDT on soil microflora with special reference to soil algae and algal transformation of DDT

DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) and its principle metab olites, DDE (I,1-dichloro-2,2-bis(p-chlorophenyl)ethylene) and DDD (1,1-dic hloro-2,2-bis(p-chlorophenyl)ethane) are widespread environmental contamina nts but little information is available concerning their effects on non-tar get microflora (especially microalgae and cyanobacteria) and their activiti es in long-term contaminated soils. For this reason a long-term DDT-contami nated soil was screened for DDT residues and toxicity to microorganisms (ba cteria, fungi, algae), microbial biomass and dehydrogenase activity. Also, five pure cultures isolated from various sites (two unicellular green algae and three dinitrogen-fixing cyanobacteria) were tested for their ability t o metabolise DDT. Viable counts of bacteria and algae declined with increas ing DDT contamination while fungal counts, microbial biomass and dehydrogen ase activity increased in medium-level contaminated soil (27 mg DDT residue s kg(-1) soil). All the tested parameters were greatly inhibited in high-le vel contaminated soil (34 mg DDT residues kg(-1) soil). Species composition of algae and cyanobacteria was altered in contaminated soils and sensitive species were eliminated in the medium and high contaminated soils suggesti ng that these organisms could be useful as bioindicators of pollution. Micr obial biomass and dehydrogenase activity may not serve as good bioindicator s of pollution since these parameters were potentially influenced by the in crease in fungal (probably DDT resistant) counts. All the tested algal spec ies metabolised DDT to DDE and DDD; however, transformation to DDD was more significant in the case of dinitrogen-fixing cyanobacteria. (C) 2000 Elsev ier Science Ltd. All rights reserved.