Earthworms and the dissipation and distribution of atrazine in the soil profile

The influence of earthworms (Lumbricus terrestris L.) on the persistence and transport of C-14-labelled atrazine [2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine] in soil was studied in laboratory incubations using flask microcosms and packed columns. In soil microcosm incubations (12 or 30 degrees C), [U-ring-C-14]atrazine was dissipated and mineralized more rapidly in soil that had been conditioned (preincubated) with earthworms (e.g, soil containing worm castings) than in soil without earthworms. Earthworms added to soil following herbicide application accelerated the formation of non-extractable (soil-bound) atrazine residues and reduced atrazine mineralization rates over 68 d, compared to soil that did not contain earthworms. In packed soil columns (24 cm x 6.3 cm i.d,), earthworms promoted the formation of non-extractable residues and modified the vertical distribution of herbicide residues, Following a 68-d incubation of soil columns (12 degrees C) receiving a surface application of [U-ring-C-14]atrazine-sprayed corn leaves, total non-extractable radioactivity in soil columns containing earthworms was 21%; greater than that in soils without earthworms. Earthworm consumption of the [U-ring-14C]atrazine-sprayed corn leaves and subsequent activity translocated 60% of the total radioactivity below 4 cm, In contrast, more than 65% of the initially applied [U-ring-C-14]atrazine remained in the top 3 cm surface layer in columns containing no earthworms. Earthworms also influenced the distribution of herbicide residues in the soil matrix, depositing about twice as much MeOH-extractable radioactivity in their burrow linings as in the surrounding soil. Crown Copyright (C) 2000 Published by Elsevier Science Ltd. All rights reserved.