Biobeds for Azoxystrobin and Imidacloprid Rinsate Disposal
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Date
2018
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DIVISION OF AGRICULTURAL CHEMICALS ICAR-INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI –
Abstract
Improper disposal of leftover pesticide from sprayer operation or cleaning and spills during
sprayer filling can contaminate soil and water bodies. The biobed, which contain a
biologically active biomixture, provides a simple low cost method for on-farm treatment of
pesticide wastes. The composition and properties of a biomixture used in a biobed are
decisive for pesticide sorption and degradation. Four rice straw (RS)/corn cob (CC) and peat
(P)/compost (C) based biomixtures viz. RS+C, RS+P, CC+P and CC+C, were used to study
adsorption and degradation of azoxystrobin and imidacloprid.
The kinetics and adsorption of azoxystrobin and imidacloprid on biomixtures was
studied using batch method. The kinetics data was modelled using pseudo first-order (PFO),
pseudo second-order (PSO), Elovich and intra-particle diffusion (IPD) models. Results (r2
Adj
values) suggested that modified Elovich model was the best suited to explain the kinetics of
imidacloprid sorption while different models explained azoxystrobin sorption kinetics in
different biomixtures (PFO in RS+C and RS+P; PSO in CC+P and Elovich in CC+C).
Biomixtures varied in their capacity to adsorb both pesticides and the adsorption coefficient
(Kd) values were 116.8-369.24 (azoxystrobin) and 24.2-293.4 (imidacloprid). Compared to
the Langmuir isotherm the Freundlich isotherm better explained the adsorption of both
pesticides. Comparison analysis of the linear and nonlinear method for estimating the
Freundlich adsorption constants suggested that the nonlinear Freundlich equation better
explained the adsorption.
Degradation of azoxystrobin and imidacloprid in biomixtures was studied and role of
biomixture conditioning, moisture content and pesticide concentration was evaluated. Results
indicated that biomixture condition affected pesticide degradation, but effect was significant
on imidacloprid degradation where 2.5 to 9 times decrease in half-life were observed.
Increasing the moisture content from 60% to 80% water holding capacity increased
degradation of both pesticides. Degradation of both pesticides slowed down with increase in
the initial concentration in biomixtures. Conditioning of biomixture increased microbial
biomass carbon (1.2 - 4 times) and dehydrogenase activity (9-16 times). Azoxystrobin and
imidacloprid application showed no adverse effect on the microbial biomass carbon,
dehydrogenase and fluorescein diacetate activity.
Retention and degradation of azoxystrobin and imidacloprid was studied in the
constructed biobeds using RS+C and CC+C biomixtures and 2 applications of mixture of both
pesticides (10,000 µg each) at 45 days intervals were made. None of the pesticide was
detected in the leachate. Imidacloprid was completely degraded after both applications in both
biobeds, while azoxystrobin did not degrade completely. Out of total 20,000 µg of
azoxystrobin applied 81.5 and 68.1% was degraded in the RS+C and CC+C biobeds,
respectively. Except for inhibition of the dehydrogenase activity in the CC+C biobed, no
adverse effect of pesticide application on microbial parameters was observed. The study
suggested that pesticide degradation was affected by the biomixture conditioning, moisture
level and pesticide concentration. The RS+C biomixture, prepared using low cost and easily
available materials, can be used in depuration systems for pesticide rinsate disposal.
Keywords : Azoxystrobin, Imidacloprid Rinsate, Biomixtures, Dehydrogenase
Description
t-10043
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