Changes in microbial properties associated with long-term arsenic and DDT contaminated soils at disused cattle dip sites

This work examined the effect of long-term arsenic (As) and DDT contamination on soil microbial properties at 11 cattle dip sites in northern New South Wales, Australia. Total As in the surface (0–10 cm) soils from these sites ranged from 34 to 2941 mg As kg−1 soil and hexane-extractable DDT concentrations ranged between 2.9 and 7673 mg DDT kg−1 soil. The concentrations of water and oxalate-extractable As were positively correlated with total As. Oxalate-extractable As was more strongly correlated (r2=0.87) with total As than water-extractable As (r2=0.34). A weak positive relationship was observed between the level of nutrient (organic carbon and nitrogen) and microbial biomass C (r2=0.61 and 0.45, respectively). There was a highly significant difference between the microbial properties of polluted and unpolluted sites (P<0.001). In comparison to unpolluted soils, fungal counts, microbial biomass C, and respiration were dramatically reduced (P<0.05) in polluted soils. However, the bacterial population between polluted and unpolluted soils were not different (P<0.05). The results of this study suggested that (a) long-term contamination of soils adjacent to former cattle dipping sites by As and DDT adversely affected soil microbial properties with the fungal populations being the most sensitive and (b) there was little regeneration of microbiota despite 25 years of field ageing of the soils.