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

The influence of earthworms (Lumbricus terrestris L.) on the persistence an d transport of C-14-labelled atrazine [2-chloro-4-ethylamino-6-isopropylami no-1,3,5-triazine] in soil was studied in laboratory incubations using flas k microcosms and packed columns. In soil microcosm incubations (12 or 30 de grees C), [U-ring-C-14]atrazine was dissipated and mineralized more rapidly in soil that had been conditioned (preincubated) with earthworms (e.g, soi l containing worm castings) than in soil without earthworms. Earthworms add ed to soil following herbicide application accelerated the formation of non -extractable (soil-bound) atrazine residues and reduced atrazine mineraliza tion 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 formatio n of non-extractable residues and modified the vertical distribution of her bicide residues, Following a 68-d incubation of soil columns (12 degrees C) receiving a surface application of [U-ring-C-14]atrazine-sprayed corn leav es, total non-extractable radioactivity in soil columns containing earthwor ms was 21%; greater than that in soils without earthworms. Earthworm consum ption of the [U-ring-14C]atrazine-sprayed corn leaves and subsequent activi ty translocated 60% of the total radioactivity below 4 cm, In contrast, mor e than 65% of the initially applied [U-ring-C-14]atrazine remained in the t op 3 cm surface layer in columns containing no earthworms. Earthworms also influenced the distribution of herbicide residues in the soil matrix, depos iting about twice as much MeOH-extractable radioactivity in their burrow li nings as in the surrounding soil. Crown Copyright (C) 2000 Published by Els evier Science Ltd. All rights reserved.