Environ. Sci. Technol. 2002, 36, 683-689
Characterization of the Atrazine’s Bound (Nonextractable) Residues Using Fractionation Techniques for Soil Organic Matter LUDOVIC LOISEAU AND ENRIQUE BARRIUSO* UMR INRA-INA PG Environnement et Grandes Cultures, 78850 Thiverval-Grignon, France
Atrazine’s bound residues (BR), in the range of 10-40% of the applied atrazine, were obtained by laboratory incubation (56 d) of four soils having different capacities to degrade atrazine in relation to the presence or absence of a microflora able to mineralize the triazinic ring. Soil size fractionation followed by alkaline extraction, before and after HF treatment, and then acid hydrolysis with 2 M HCl in reflux conditions was applied to the soils containing BR. Most of the BR were in the finest fraction (50 µm, was separated from the “mineral” fractions (>50 µm), called Min >50 µm, by flotation (21). Alkaline Extractions. A total of 15 g of the fraction (50 µm
20-50 µm
75% of the initial atrazine in soil MG8; an initial lag phase of 4 d followed atrazine mineralization at a continuous low rate in WG8 and MV6 soils; and an intermediary fate in MS5 soil. At the end of incubation, the total atrazine mineralized ranged between 84 and 10% in the following decreasing order: MG8 > MS5 > WG8 > MV6 (Table 2). The soils that mineralized the most atrazine were the soils that were treated with atrazine every year in field conditions (MG8 and MS5 as compared to WG8 VOL. 36, NO. 4, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 4. Enrichment factor of bound residues and soil carbon in relation to soils size fractions (enrichment factor is defined as the ratio of the content in the fractions to the content of the whole soil). and MV6), and the soils with the highest pH (MG8 as compared to MS5; WG8 as compared to MV6). The total extractable residues (water plus methanol extracts) ranged between 4 and 50%. Atrazine was found in all extracts, representing 1% of the initial atrazine when mineralization was high in MG8 soil and about 10% in the other three soils (Table 2). Dealkylated derivatives were in the same proportions as atrazine. They were the predominant compounds in the extracts of WG8 soil, whereas hydroxylated derivatives represented the largest metabolite fraction in MV6 soil. The BR amount ranged between 40 and 10% of the initial atrazine (Table 2). The proportion of BR decreased in the following order: MV6 > WG8 > MS5 > MG8, which is the inverse order of those of mineralization rates. 14C-Bound Residues and Carbon Distributions in Particle Size Fractions. Between 37 and 63% of the mass of different soils was in the fraction 60% of total BR) was also in the fractions 50 and 50 µm fractions of MG8 and WG8 for C was 2 and 1.8, respectively, whereas it was only 0.3 for BR. This result could indicate that the organic matter in the Min >50 µm fraction of MG8 and WG8 is less efficient than the organic matter of the LOM >50 and
