Release of Soil-Bound Prometryne Residues Under Different Soil pH and Nitrogen Fertilizer Regimes

248

181

The analysis of the coherent data on nonextractable (bound) residues (NER) from the literature and EU pesticide registration dossiers allows the identification of general trends, in spite of the large variability and heterogeneity of data. About 50% of the pesticides reviewed exhibit a low proportion of NER (less than 30% of the initial amount) while only 12% of pesticides have a proportion of NER exceeding 70%. The lowest proportion of NER was found for dinitroanilines (<20%), and the largest value was obtained for carbamates, and in particular dithiocarbamates. The presence of chemical reactive groups, such as aniline or phenol, tends to yield a larger proportion of NER. NER originating from N-heteroatomic ring were found to be lower than those from phenyl-ring structures. Among the environmental factors affecting the formation of NER, microbial activity has a direct and significant effect. Concerning the NER uptake or their bioavailability, consistent data suggest that only a small percentage of the total amounts of NER can be released. The analysis of NER formation kinetics showed that incubation experiments are often stopped too early to allow a correct evaluation of the NER maturation phase. Therefore, there is a need for longer term experiments to evaluate the tail of the NER formation kinetics. Still, the heterogeneity of the NER data between pesticides and for specific pesticides calls for great care in the interpretation of the data and their generalization.

Section: Introductionmentioning

confidence: 99%

Formation of Pesticide Nonextractable (Bound) Residues in Soil: Magnitude, Controlling Factors and Reversibility

Barriuso

Benoît

Dubus

2008

248

181

“…Despite the formation of bound residues diminishing the toxicity and the bioavailability of pesticides, microbial and physicochemical release (9)(10)(11)(12)(13)(14), bioavailabilty (15)(16)(17), plant uptake (14,18,19), and uptake by earthworms (14) of BR have all been demonstrated. Generally, values observed for release, bioavailabilty, and uptake ranged over a small percentage of total BR, but they show that they are not entirely excluded from environmental interaction and that further research in the characterization of BR as the mechanisms involved in their formation are needed to better predict their potential hazards.…”

Section: Introductionmentioning

confidence: 99%

Characterization of the Atrazine's Bound (Nonextractable) Residues Using Fractionation Techniques for Soil Organic Matter

Loiseau

Barriuso

2002

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 (<20 microm) that contained the humified organic matter (from 61 to 77% of the total BR), and between 78 and 89% was made soluble during the different steps of the chemical fractionation procedure. From 20 to 50% of the BR of the fraction <20 microm was identified as the intact atrazine and its main derivatives, indicating that this proportion of the BR was probably formed by entrapment in voids of the soil organic matter. Between 13 and 30% of the BR was associated to humic acids (HA); they were not dialyzable and were released by acid hydrolysis with HCl, indicating that these BR were chemically bound to HA by an heteroatomic bond after the substitution of the chlorine atom of atrazine. Comparison of the results obtained for the four soils indicated that (i) an important activity of microorganisms able to mineralize the triazinic ring favors the formation of highly degraded products that can form BR; (ii) a soil pH <6 favors the formation and stabilization of hydroxylated derivatives of atrazine, and (iii) a high content of humic acids favors the formation of chemically bound residues.

“…The rhizosphere characteristics of soil texture, pH, and root exudates could control the fractions of organic pollutants . In this study, chemical analysis of soil texture characteristics (e.g., clay, silt, and sand contents) did not reveal significant differences after rice planting, and pH values in soil were reduced by only 0.1–0.3 pH units in root and 1 mm compartments after cultivation (data not shown).…”

Section: Resultsmentioning

confidence: 59%

Fractions Transformation and Dissipation Mechanism of Dechlorane Plus in the Rhizosphere of the Soil–Plant System

Cheng

Ding

Liang

et al. 2020

The fractions transformation and dissipation mechanism of Dechlorane Plus (DP) in the rhizosphere of soil− plant system were investigated and characterized by a 150-day experiment using a rhizobox system. The depuration, accumulation, and translocation of DP in rice plants were observed. The contributions of plant uptake, microbial degradation, and boundresidue formation to DP dissipation under the rhizosphere effect were modeled and quantified. The gradients of DP concentrations correlated well with microbial biomass in the rhizosphere (R 2 = 0.898). The rhizosphere facilitated the bioavailability of DP (excitation) and modified the bound-residue formation of DP (aging). DP concentrations in roots were positively correlated with the labile fraction of DP in soil (R 2 = 0.852−0.961). There were spatiotemporal variations in the DP fractions. Dissolved and soil organic carbon were important influences on fraction transformation. Contributions to total DP dissipation were in the following ranges: microbial degradation (8.33−54.14%), boundresidue formation (3.64−16.43%), and plant uptake (0.54−3.85%). With all of these processes operating, the half-life of DP in the rhizosphere was 105 days. The stereoselectivity of DP isomers in both rice and DP fractions in soil were observed, suggesting a link between stereoselective bioaccumulation of DP in terrestrial organisms and dissipation pathways in soil.