Arne Helweg

Degradation and adsorption of 14C-mecoprop (MCPP) in surface soils and in subsoil. Influence of temperature, moisture content, sterilization and concentration on degradation

Degradation and adsorption of 14C-ringlabelled mecoprop was determined in three different soil types under different environmental conditions. Degradation was also determined in subsurface soil. The adsorption of MCPP was low with Kd-values of 0.1–0.2 and Koc-values of 8, 13 and 5, respectively in the three soil types. The correlation between mecoprop disappearance at 2 mg kg−1 and 14CO2-evolution showed that when 12% 14C was evolved as 14CO2, half of the mecocrop was decomposed. Estimated half-life times in the three surface soils were 3, 3 and 4 days, respectively at 20°C. When the degradation was determined at 20, 10 and 5°C the estimated half-life was 3, 12 and 20 days, respectively. The degradation rate of mecoprop increased initially with a doubling time of 1.4, 4.9 and 6.9 days, respectively at 20, 10 and 5°C but with a 14-day lag-phase at 5°C. In dry and in flooded soil (25 and 200% of total water holding capacity) estimated half lives were 10 and 15 days, respectively. At 0.2 mg kg−1 the half-life was 1.3 days compared to the 3 days at 2 mg kg−1. In sterile soil no degradation was observed. In soil sampled at 0–33, 33–66 and 66–99 cm depth the estimated half-life time of mecoprop (0.05 mg kg−1) was 7, 70 and 34 days, respectively at 10°C.

Pollution at and below Sites used for Mixing and Loading of Pesticides

Sites used for mixing and loading of pesticides in sprayers and for washing tractors and sprayers may be point sources of pesticides. Pollution may be caused by accidental spills during filling, disposal of excess spray solution, rinsing of sprayer and tractor or from leaking nozzles on the sprayer. Ground water sampled 2-4 m below sites used for mixing and loading has been analysed for 23 or 46 different pesticides and metabolites in two Danish counties (Storstrøm and Bornholm). Further, the surface pollution at sites used for mixing, loading and rinsing was determined by elution with water of soil sampled in the top 10 cm. In all ground water samples pesticide pollution was determined to be above the European drinking water level (0.1 µg L m 1 ). The highest concentrations and most pesticides were found below loading and mixing sites at machine pools, where the highest concentrations were the phenoxyacid herbicides dichlorprop (750 µg L m 1 ) and 2,4-D (800 µg L m 1 ). The herbicides bentazone, mecoprop and dinoseb were also found in relatively high concentrations (5-60 µg L m 1 ). The surface soil sampled at the top 0-10 cm at sites used for loading and washing sprayers at six farms was eluted with water. These analyses also showed that many different pesticides and relatively high concentrations could be leached out from the soil. Twenty-four different pesticides and metabolites were found, and though most concentrations were below 10 µg L m 1 about 10% of the water samples contained more than 50 µg L m 1 . The results demonstrate that sites used for mixing, loading and washing can be seriously contaminated with pesticides even in ground water 2-4 m below the sites. This implies that ground water, nearby wells and well borings are at risk of pollution and indicates the need for better farm practice.

Degradation of mecoprop at different concentrations in surface and sub-surface soil

Biodegradation of [ring- 14 C] mecoprop (2-(4-chloro-2-methylphenoxy) propionic acid) was determined in surface and sub-surface soil at concentrations of 0.0005, 0.05, 0.5, 5, 50, 500, 5000 and 25 000 mg kg -1 . The kinetics of mineralisation were evaluated from the mineralisation rates as a function of time and by non-linear regression analysis. In the sub-surface soil, degradation was 6-8 times slower than in surface soil, but the shape of the curves was the same in both layers. At concentrations between 0.0005 and 0.5 mg kg -1 , in both surface and sub-surface soil, degradation was initially zero-order followed by first-order kinetics. At 5 to 500 mg kg -1 in surface soil and 5 to 50 mg kg -1 in sub-surface soil the degradation rate was initially either constant or decreasing followed by exponential degradation indicating increasing populations of mecoprop decomposers in the soil. At 5000 and 25 000 mg kg -1 in the surface soil and at 500, 5000 and 25 000 mg kg -1 in the sub-surface soil, the degradation was negligible, as determined by the percentage [ 14 C] carbon dioxide evolved. By non-linear regression, the three-half order model was found to describe the mineralisation.

Degradation of Mecoprop and Isoproturon in Soil Influence of Initial Concentration

Abstract Models used to describe rates of degradation are presented and exemplified, and data from mecoprop at 0.0005 to 5000 mg kg−1 and isoproturon at 0.001 to 5000 mg kg−1 were tested in the models. Degradation was described by evolution of 14CO2 from 14C-labelled pesticides incubated in soil sampled in plough layer and in subsurface. For mecoprop the degradation rate of 0.0005 mg kg−1 followed first-order models in both plough layer and in subsoil. At 5 mg kg−1 the degradation showed kinetics with exponential growth in both surface and subsoil. At 5000 mg kg−1 the degradation was very slow. The degradation of isoproturon at all concentrations and soil types followed kinetics without growth of microorganisms. The model that gave the best fit for degradation of isoproturon was a three-half order model consisting of one first-order process and one of zero-order. The rate of degradation for both pesticides and soil types was highest at the low concentrations, whereas at 5000 mg kg−1 the degradation was ve...

Degradation of [14C]ethylenethiourea in surface and subsurface soil

Abstract Degradation of 0.07 mg/kg 14 C-labelled ethylenethiourea (ETU) was determined in surface and subsurface in coarse sandy field soil from Denmark. Surface soil from 15 cm depth was sieved and incubated in Erlenmeyer flasks at 21°C. Subsurface soil from 60 and 100 cm depth was incubated as undisturbed soil cores in steel tubes at 10°C. The effect of incubation in undisturbed or mixed samples were determined. The mineralization of ETU in surface soil was rapid: 19.5 ± 4% of added 14 C was evolved as 14 CO 2 after 24 h of incubation. In subsurface soil an overall lower rate of mineralization of ETU was found, and at 100 cm depth mineralization was slower than at 60 cm; 16.3 ± 4.1% and 23.5 ± 3.8% of added 14 C being evolved as 14 CO 2 after 109 days of incubation, respectively. Exponentially increasing evolution of 14 CO 2 indicating proliferation of decomposers was seen in most samples from both surface and subsurface soil samples. The slow degradation of ETU in subsurface soil compared with surface soil implies a greater risk of groundwater contamination once ETU has leached to the subsurface.