Leaching of Pesticides from Biobeds:  Effect of Biobed Depth and Water Loading

Abstract

Pesticides may be released to farmyard surfaces as a result of spillages, leakages, and the decontamination of tractors and sprayers. Biobeds can be used to intercept and treat contaminated runoff, thus minimizing losses to the environment. Previous studies using lined and unlined biobeds showed that water management was the limiting factor for both systems. While lined biobeds effectively retained pesticides, the system rapidly became water logged and degradation was slow. Studies using unlined biobeds showed that >99% of the applied pesticides were removed by the system, with a significant proportion degraded within 9 months. However, peak concentrations of certain pesticides (Koc < 125) were unacceptable to the regulatory authorities. These experiments were designed to optimize the design and management of unlined biobeds. Experiments performed to investigate the relationship between biobed depth and water loading showed that biobeds need to have a minimum depth of 1-1.5 m. The surface area dimension of the biobed depends on the water loading, which is controlled by the nature and frequency of pesticide handling activities on the farm. Leaching losses of all but the most mobile (Koc < 15) pesticides were <0.32% of the applied dose from 1.5 m deep biobeds subject to a water loading of 1175 L m(-2). These were reduced to <0.06% when a water loading of 688 L m(-2) was applied and down to <0.0001% for a water loading of 202 L m(-2). On the basis of these data, a 1.5 m deep biobed, subject to a maximum water loading of 1121 L m(-2) and with a surface area of 40 m(2) should be able to treat < or =44000 L of pesticide waste and washings such that the average concentration of all pesticides, other than those classified as very mobile, does not exceed 5 microg L(-1). This level of treatment can be improved by further reduction in the hydraulic loading.

Overview of on‐farm bioremediation systems to reduce the occurrence of point source contamination

“…However, if the system has to treat dilute pesticide waste and equipment washings, as in the UK, it must cope with large volumes of rest and cleaning waters. In the study of Fogg et al ,62 three different hydraulic loadings were tested: direct rainfall, 2797 L m −2 and 9747 L m −2 . Pesticide leaching was clearly affected by the hydraulic loading (Table 3—parameter: influence of water loading).…”

Degradation and adsorption of terbuthylazine and chlorpyrifos in biobed biomixtures from composted cotton crop residues

“…Although biobeds were initially introduced in Sweden, several modifications of the prototype have been tested extensively in other northern European countries including the United Kingdom,7 Denmark8 and Belgium 9. Their high efficacy and ease in construction and use facilitated their recent introduction also into Latin American countries including Peru, Ecuador and Guatemala 10.…”

Mineralisation and degradation of 2,4‐dichlorophenoxyacetic acid dimethylamine salt in a biobed matrix and in topsoil

“…Although 2,4‐D degradation in a biobed matrix have not been reported in the literature, the results obtained from our experiments involving single and repeated additions of 2,4‐D DMA are in agreement with those for other pesticides. For example, more than 99% of applied amounts of malathion and glyphosate and >98% of isoproturon, dimethoate and mecoprop‐P were degraded in biobed matrices within 6 and 12 months respectively. Fogg et al reported greater degradation of six pesticides (isoproturon, chlorothalonil, pendimethalin, chlorpyrifos, epoxiconazole and dimethoate) in a single addition to a biobed matrix compared with topsoil.…”