Mineralization of aged atrazine and mecoprop in soil and aquifer chalk

The effect of ageing on the bioavailability and sorption of the herbicides atrazine and mecoprop was studied in soil and aquifer chalk sampled at an agricultural field near Aalborg, Denmark. The herbicides were incubated in sterile soil or chalk up to 3 months prior to inoculation with 5×10⁷ cells g^-1 (dry weight) of a mecoprop degrading highly enriched culture (PM) or 1×10⁹cells g^-1 (dry weight) of the atrazine degrading Pseudomonas sp. strain ADP. As a measure of the bioavailable residues accumulated ¹⁴CO₂ was measured for 2 months. In both soil and chalk ageing limited the rate of atrazine mineralization, and in chalk the extent of mineralization was reduced as well. The fraction of sorbed atrazine in the soil ranged between 50% and 62%, whereas a maximum of 12% was sorbed in chalk. No impact on the mineralization of aged mecoprop was seen as no sorption of this herbicide on either soil or chalk was measured.