MODIFICATIONS TO ATRAZINE DEGRADATION PATHWAYS IN A LOAMY SOIL AFTER ADDITION OF ORGANIC AMENDMENTS

The effects of two organic amendments, a municipal solid waste compost and a composted straw, on [U-ring-C-14]atrazine degradation pathways in a loamy soil (Grignon, Yvelines, France) were studied during labora tory incubations under controlled conditions. Three month conditioning s were conducted under sterile or non-sterile conditions, with soil pl us atrazine, organic amendment plus atrazine, or soil plus organic ame ndment. Then either an organic amendment or soil or atrazine was added , respectively, to these three treatments and incubated for an additio nal 3 months under non-sterile conditions. Both organic amendments mod ified the behaviour of atrazine in soil but via different processes. T he addition of municipal compost increased atrazine sorption and decre ased its availability for degradation by soil microorganisms. The effe ct of the composted straw was mainly related to its high enzymatic act ivity, which appeared to be responsible for the production of large am ounts of hydroxyatrazine. This hydroxylation favoured the opening of t he triazine ring and its subsequent mineralization in the soil. At the end of the incubations, less atrazine was mineralized in the presence of the two types of organic amendment, which both increased the forma tion of non-extractable residues of atrazine. The addition of municipa l compost preserved larger amounts of extractable atrazine, while the addition of composted straw enhanced hydroxyatrazine production. In al l cases, the greatest effects were found when atrazine was directly in contact with the organic amendment during conditioning. (C) 1998 Else vier Science Ltd. All rights reserved.