Atrazine degradation in sub-soils
Atrazine has been one of the most successful herbicides used both in agriculture and in urban situations. Its use has now been banned in U.K. agriculture. Atrazine applied to agricultural soils has been shown to leach down the profile with residues remaining in the soil up to 9 years after initial application. Residues are frequently found in sub-soils and aquifers world wide. In this study, systems were developed that enabled sampling and incubation of intact sub-soils cores that contained a sub-soil atmosphere. The sub-soil represents the last zone of significant potential degradation of xenobiotics, such as atrazine, as leaching into deeper soils and ground waters occurs. Conditions prevailing in these soils are different in terms of soil atmosphere, structure and activities of the soil microbial community. Laboratory studies were carried out which investigated the rate of atrazine mineralisation in intact sub-soil cores. Soil cores were aerated with either laboratory air or CO2-rich air generated through soil microbial activity from within a sealed sub-soil air reservoir. Results showed that atrazine mineralisation occurred at significantly higher rates in sub-soil cores aerated with sub-soil air compared to the rates in sub-soil cores aerated with laboratory air. Studies comparing mineralisation rates in intact sub-soil cores, incubated under sub-soil air or labroatory air, and soil biometers, containing sieved, mixed sub-soil, showed that higher rates of atrazine mineralisation occurred in the biometer studies than occurred in intact sub-soil cores. Similar studies using intact top-soil cores showed higher rates of mineralisation. Investigations carried out using intact sub-soil cores amended with a range of glucose concentrations, showed that no difference occurred in glucose mineralisation rates between soil cores aerated under sub-soil air and under laboratory air.