Pesticide Adsorption as a Function of Depth below Surface

The adsorption of atrazine and mecoprop to soil at different levels below the surface was measured and compared with values calculated from the partition coefficient—between soil organic carbon and water—and the carbon content. With soil samples from the top layers, the calculated values were in fairly good agreement with the measured values. Below the top layers, the importance of the effect of clay content on the adsorption is reflected in the difference between the measured and calculated K_d values. Calculated values can be unrealistically low resulting in overestimates of leaching. © 1997 SCI.     

Leaching of atrazine into ground water

A study of the leaching of atrazine from soils in Denmark with high hydraulic conductivity demonstrated only small quantities of the herbicide in the upper ground-water zone. The atrazine-treated fields were situated in a region where the water table was high and free lying and where the cover layer consisted of sand. Samples were taken from the upper 1–5 m ground-water zone at three well-defined levels. The atrazine content was between 0.01 and 0.05 μg litre^?1 the highest concentrations being found at the top of the ground-water zone.     

Leaching of atrazine and hexazinone from Abies nordmanniana (Steven) spach plantations

The content of the herbicides atrazine and hexazinone was measured in drainage water from seven to ten-year-old plantations grown with Abies nordmanniana (Steven) Spach on two clayey soils in Denmark. The concentrations of atrazine varied between 0.06 and 7.79 μg litre^?1. The concentrations of hexazinone were different at the two locations, ranging from 0.07 to 2.09 μg litre^?1 at Bremersvold and from 3.47 to 42.66 μg litre^?1 at Koege. Metabolites of both herbicides were identified.     

Monitoring Methyl Tertiary Butyl Ether (MTBE) and other Organic Micropollutants in Groundwater: Results from the Danish National Monitoring Program

The paper presents results of analyses of 7671 groundwater samples collected from 1115 screens in the period 1993 to 2001 for the Danish National Groundwater Monitoring Program. In Denmark groundwater is widely used for drinking water and the objectives of the monitoring program is to describe the present conditions, the development of, and the impacts on the groundwater. The design of the Danish National Groundwater Monitoring Program is described and data are provided. Data originate from monitoring areas and are supplemented with data from the waterworks' control of nearly 6000 water supply wells. In addition to pesticides there is a series of other organic compounds that must be considered in relation to possible groundwater contamination. Sources of these compounds and their importance in relation to groundwater contamination is discussed on the basis of the monitoring data. The organic micropollutants monitored are grouped according to chemical properties: aromatic hydrocarbons, chlorophenols, detergents, halogenated aliphatic hydrocarbons, ethers (MTBE), phenols, and phthalates. The most frequently found compounds were toluene (18.7% ), phenol (14.6%), xylene (10.9), trichloromethane (9.5%), and benzene (in 8.8% of the screens monitored). The five compounds most frequently found at a concentration above the maximum residue limits (MRL) for drinkingwater were: dibuthylphthalate (28%), phenol (14%), 2,4-dichlorophenol (10%), trichloromethane (10%), pentachlorophenol (7% of findings exceeding the MRL for drinkingwater). Overall, one or several compound was observed at least once in 57.8% of the 1115 screens monitored within the period 1993–2001. On a yearly basis the median finding frequency was 19%.     

Capacity of model biobeds to retain and degrade mecoprop and isoproturon

Biobeds are used to increase the adsorption and degradation of pesticide spillage on sites used for mixing and loading and for cleaning of sprayers. The adsorption and the rate of degradation of 14C-labelled isoproturon and mecoprop (MCPP) at concentrations from 0.0005 to 25 000 mgkg(-1) were determined in biobed soil. Further leaching of the two herbicides was determined in a model biobed with a surface area of 2 m2. The biobed material showed enhanced ability to adsorb the two herbicides. Kd was 5.2 litre kg(-1) for isoproturon and 1.6 litre kg(-1) for MCPP in biobed material, which is higher than in natural soil. In different experiments with natural soil, Kd ranges from 0.07 to 0.6 litrekg(-1) for MCPP and from 1.5 to 4.6 litre kg(-1) for isoproturon in soils with varying organic carbon content. Degradation of MCPP was rapid at concentrations from 0.0005 to 500 mg kg(-1), delayed at 5000 mg kg(-1), and very slow at 25 000 mg kg(-1). For isoproturon, the relative degradation was most rapid at the lowest concentration and decreasing with increasing concentrations. After 120 days, between 55% and 8% 14C was evolved as 14CO2 at concentrations between 0.0005 and 25 000 mg kg(-1). The rate of evolution of 14CO2 indicated that degradation rates at low concentrations were of first-order and at higher concentrations of zero-order. Leaching of MCPP and isoproturon was determined in a newly established model biobed during a 2-year period. About 13% of applied MCPP and 1.4% of applied isoproturon leached out during the winter following the first autumn application (worst-case scenario). Leaching was completely prevented when the biobed had a well-developed grass cover and was covered during the winter.