Jeanne Kjær

Transport modes and pathways of the strongly sorbing pesticides glyphosate and pendimethalin through structured drained soils

Leaching of the strongly sorbing pesticides glyphosate and pendimethalin was evaluated in an 8-month field study focussing on preferential flow and particle-facilitated transport, both of which may enhance the leaching of such pesticides in structured soils. Glyphosate mainly sorbs to mineral sorption sites, while pendimethalin mainly sorbs to organic sorption sites. The two pesticides were applied in equal dosage to a structured, tile-drained soil, and the concentration of the pesticides was then measured in drainage water sampled flow-proportionally. The leaching pattern of glyphosate resembled that of pendimethalin, suggesting that the leaching potential of pesticides sorbed to either the inorganic or organic soil fractions is high in structured soils. Both glyphosate and pendimethalin leached from the root zone, with the average concentration in the drainage water being 3.5 and 2.7 μg L(-1), respectively. Particle-facilitated transport (particles >0.24 μm) accounted for only a small proportion of the observed leaching (13-16% for glyphosate and 16-31% for pendimethalin). Drain-connected macropores located above or in the vicinity of the drains facilitated very rapid transport of pesticide to the drains. That the concentration of glyphosate and pendimethalin in the drainage water remained high (>0.1 μg L(-1)) for up to 7d after a precipitation event indicates that macropores between the drains connected to underlying fractures were able to transport strongly sorbing pesticides in the dissolved phase. Lateral transport of dissolved pesticide via such discontinuities implies that strongly sorbing pesticides such as glyphosate and pendimethalin could potentially be present in high concentrations (>0.1 μg L(-1)) in both water originating from the drainage system and the shallow groundwater located at the depth of the drainage system.

Comparative Mapping of Soil Physical–Chemical and Structural Parameters at Field Scale to Identify Zones of Enhanced Leaching Risk

Preferential flow and particle-facilitated transport through macropores contributes significantly to the transport of strongly sorbing substances such as pesticides and phosphorus. The aim of this study was to perform a field-scale characterization of basic soil physical properties like clay and organic carbon content and investigate whether it was possible to relate these to derived structural parameters such as bulk density and conservative tracer parameters and to actual particle and phosphorus leaching patterns obtained from laboratory leaching experiments. Sixty-five cylindrical soil columns of 20-cm height and 20-cm diameter and bulk soil were sampled from the topsoil in a 15-m × 15-m grid in an agricultural loamy field. Highest clay contents and highest bulk densities were found in the northern part of the field. Leaching experiments with a conservative tracer showed fast 5% tracer arrival times and high tracer recovery percentages from columns sampled from the northern part of the field, and the leached mass of particles and particulate phosphorus was also largest from this area. Strong correlations were obtained between 5% tracer arrival time, tracer recovery, and bulk density, indicating that a few well-aligned and better connected macropores might change the hydraulic conductivity between the macropores and the soil matrix, triggering an onset of preferential flow at lower rain intensities compared with less compacted soil. Overall, a comparison mapping of basic and structural characteristics including soil texture, bulk density, dissolved tracer, particle and phosphorus transport parameters identified the northern one-third of the field as a zone with higher leaching risk. This risk assessment based on parameter mapping from measurements on intact samples was in good agreement with 9 yr of pesticide detections in two horizontal wells and with particle and phosphorus leaching patterns from a distributed, shallow drainage pipe system across the field.

Leaching of azoxystrobin and its degradation product R234886 from Danish agricultural field sites.

The objective was to estimate leaching of the fungicide azoxystrobin (methyl (αE)-2-[[6-(2-cyanophenoxy)-4-pyrimidinyl]oxy]-α-(methoxymethylene)benzene-acetate) and one of its primary degradation products R234886 ([(E)-2-(2-[6-cyanophenoxy)-pyrimidin-4-yloxyl]-phenyl-3-methoxyacrylic acid], major fraction) at four agricultural research fields (one sandy and three loamy) in Denmark. Water was sampled from tile drains, suction cups and groundwater wells for a minimum period of two years after application of azoxystrobin. Neither azoxystrobin nor R234886 were detected at the sandy site, but did leach through loamy soils. While azoxystrobin was generally only detected during the first couple of months following application, R234886 leached for a longer period of time and at higher concentrations (up to 2.1μgL(-1)). Azoxystrobin is classified as very toxic to aquatic organisms and R234886 as very harmful. Our study shows that azoxystrobin and R234886 can leach through loamy soils for a long period of time following application of the pesticide and thereby pose a potential threat to vulnerable aquatic environments and drinking water resources. We thus recommend the inclusion of azoxystrobin and R234886 in pesticide monitoring programmes and further investigation of their long-term ecotoxicological effects.

Long-term leaching of rimsulfuron degradation products through sandy agricultural soils

The objective was to quantify leaching of the widely used low-dosage sulfonylurea herbicides rimsulfuron and its primary degradation products IN70941 ([N-(4,6-dimethoxypyrimidin-2-yl)-N-((3-ethylsulfonyl)-2-pyridinyl)urea]) and IN70942 ([N-((3-ethylsulfonyl)-2-pyridinyl)-4,6-dimethoxy-2-pyrimidineamine]) at two sandy research fields in Denmark. Water was sampled monthly from the vadose and groundwater zones at the two sites (Tylstrup and Jyndevad) over a 4-6-year period following application of rimsulfuron. No rimsulfuron was detected in the water samples. At the Jyndevad site, IN70941 was detected in the vadose zone at a depth of 1m for as long as three years in annual average concentrations exceeding the EU limit value for drinking water of 0.1microgL(-1). At the Tylstrup site, IN70941 was detected at a depth of 2m in concentrations just below 0.1microgL(-1). The groundwater concentration of IN70941 occasionally exceeded 0.1microgL(-1) at the Jyndevad site, but is only detected on one occasion (and at a low concentration) at the Tylstrup site. At both sites IN70941 was relatively stable and persisted in the soil water for several years, with relatively little degrading further to IN70942. Thus, the concentration of IN7092 was much lower and apart from four samples from the Jyndevad site, never exceeded 0.1microgL(-1). Nevertheless, our findings show that degradation products of rimsulfuron can leach through sandy soils in relatively high concentrations and could potentially contaminate vulnerable aquatic environments. In view of this risk, IN70941 and IN70942 should be included in pesticide monitoring programmes, and their long-term ecotoxicological effects should be investigated further.

Analysis of the plant growth regulator chlormequat in soil and water by means of liquid chromatography–tandem mass spectrometry, pressurised liquid extraction, and solid-phase extraction

We present a new, precise and accurate method for quantitative analysis of chlormequat in soil and aqueous matrices. The method, which is based on LC-MS/MS, pressurised liquid extraction and solid-phase extraction, is eminently suitable for studying the fate of chlormequat in the soil environment. The limit of detection is 0.003-0.008 microg/L for rainwater, surface water and groundwater and 0.07-0.4 microg/kg for soil. In water samples amended to 0.04 microg/L, precision is better than 10%. The residual content of chlormequat in three agricultural topsoils analysed 4 months after its application was 23-55 microg/kg (12-23% of the amount applied). No trace of chlormequat was detected in groundwater from 66 water supply wells located in rural areas treated with chlormequat.