DT50 Values (dt50 + value)

Distribution by Scientific Domains

Selected Abstracts

Efficiency of a bagasse substrate in a biological bed system for the degradation of glyphosate, malathion and lambda-cyhalothrin under tropical climate conditions

Laure de Roffignac
Abstract BACKGROUND: After the rinsing of spray equipment, the rinsing water contains polluting products. One way to avoid pollution is to bring the rinsing water over a purification system, a biological bed. The system consists of an impermeable tub filled with a biomix substrate that facilitates biodegradation of pesticides. Usually, straw is one component of the biomix. The objective of this study was to assess the efficiency of an unusual substrate, bagasse, a residue of sugar cane, for the degradation of three pesticides, glyphosate, malathion and lambda-cyhalothrin. RESULTS: Results showed that more than 99% of malathion and glyphosate were degraded in 6 months. In the biological bed, the DT50 value for malathion was 17 days, for glyphosate 33 days and for lambda-cyhalothrin 43 days. The degradation rate of aminomethylphosphonic acid (AMPA) residues from the degradation of glyphosate was slower than that of the other pesticides (DT50 69 days). Finally, the innocuousness of the biomix after 6 months of degradation was confirmed by biological tests. CONCLUSIONS: Although the degradation rates of the three pesticides in the present bagasse-based system were similar to those under temperate conditions, the degradation conditions were improved by comparison with those in soil under the given tropical conditions. Further benefits of this system are pesticide confinement, to avoid their dispersion in the environment by liquids or solids, and a lower overall cost. Finally, possibilities for optimising the bagasse-based system (e.g. management of the water content and nature of the biomix) are discussed. Copyright © 2008 Society of Chemical Industry [source]

Risk assessment of pesticides for soils of the central amazon, Brazil: Comparing outcomes with temperate and tropical data

Jörg Römbke
Abstract The risk of 11 pesticides to the soil environment was assessed in a 3-tiered approach at 4 sites located in Central Amazon, near Manaus, the capital of the Amazonas State in Brazil. Toxicity-exposure ratios (TERs), as routinely used for the registration of pesticides in the European Union, were calculated. First, the predicted environmental concentration (PEC) values in soil on the basis of real application rates and soil properties but temperate DT50 (degradation time of 50%) values were compared with temperate effect values (earthworm LC50s; median lethal concentrations), both gained from literature. Second, the risk assessment was refined by the use of DT50 values from tropical soils (measured for 7 compounds and estimated for 4) but still with temperate effect values because only a few results from tests performed under tropical conditions are available. Third, the outcome of this exercise was evaluated in a plausibility check with the use of the few results of effect tests, which were performed under tropical conditions. However, the lack of such data allowed this check only for 6 of 11 pesticides. The results are discussed in light of pesticide use in the Amazon in general, as well as compared with the registration status of these pesticides in other countries. Finally, suggestions are given for which kinds of studies are needed to improve the environmental risk assessment of pesticides in tropical regions. [source]

Persistence and metabolism of imidacloprid in different soils of West Bengal

A Sarkar
Abstract A laboratory experiment was performed to study the persistence of imidacloprid from two formulations (Confidor 200,g,litre,1 SL and Gaucho 700,g,kg,1 WS), and its metabolism in three different soils (Gangetic alluvial soil of Kalyani, lateritic soil of Jhargram and coastal alkaline soil of Canning) of West Bengal following application at 0.5,kg and 1.0,kg AI,ha,1. Dissipation of imidacloprid in soil followed first-order kinetics and DT50 values ranged from 28.7 to 47.8 days. The shortest half-lives (28.7 and 35.8 days) were observed in the lateritic soil of Jhargram for both liquid and powder formulations. The formation of two metabolites of imidacloprid, imidacloprid-urea and imidacloprid-olefin, was first detected on day 30 of degradation at 28,(±1),°C in all three soils. © 2001 Society of Chemical Industry [source]

Investigation of norflurazon pesticide photodegradation using plasma desorption time-of-flight mass spectrometry analysis

J.-P. Thomas
We have previously demonstrated that PD-TOFMS (plasma desorption time-of-flight mass spectrometry) analysis is a powerful technique for the in situ analysis of pesticides deposited or adsorbed on solid materials. With the aim of producing reproducible data on the modification of a pesticide under controlled photodegradation conditions, we have now undertaken a study where both the substrate and the pesticide are well characterized. This is the case for norflurazon deposited onto an aluminium substrate, in particular regarding the reproducibility of preparation of the samples and the change with time of their chemical composition. Degradation parameters have been derived from the variation in yield of ions representative of the molecule and of its breakdown products and, particularly, from the time required for 50% dissipation of their initial concentration (DT50). DT50 values ranging between 1 and 10,h have been found. An interpretation of the degradation process is proposed from the decay of other ions. As expected, the degradation is faster when the UV sunlight is unfiltered (a factor of 3.8 for the molecule, and around 5 for the breakdown products). Copyright © 2008 John Wiley & Sons, Ltd. [source]