Mecoprop Concentration Research Articles

Degradation of mecoprop in polluted landfill leachate and waste water in a moving bed biofilm reactor

Mecoprop is a common pollutant in effluent-, storm- and groundwater as well as in leachates from derelict dumpsites. Thus, bioremediation approaches may be considered. We conducted batch experiments with moving bed biofilm (MBBR)-carriers to understand the degradation of mecoprop. As a model, the carriers were incubated in effluent from a conventional wastewater treatment plant which was spiked to 10, 50 and 100 μg L−1 mecoprop. Co-metabolic processes as well as mineralization were studied. Initial mecoprop concentration and mecoprop degradation impacted the microbial communities. The removal of (S)-mecoprop prevailed over the (R)-mecoprop. This was associated with microbial compositions, in which several operational taxonomic units (OTUs) co-varied positively with (S)-mecoprop removal. The removal-rate constant of (S)-mecoprop was 0.5 d−1 in the 10 μg L−1 set-up but it decreased in the 50 and 100 μg L−1 set-ups. The addition of methanol prolonged the removal of (R)-mecoprop. During mecoprop degradation, 4-chloro-2-methylphenol was formed and degraded. A new metabolite (4-chloro-2-methylphenol sulfate) was identified and quantified.

Degradation and enantiomeric fractionation of mecoprop in soil previously exposed to phenoxy acid herbicides – New insights for bioremediation

Phenoxy acid-contaminated subsoils are common as a result of irregular disposal of residues and production wastes in the past. For enhancing in situ biodegradation at reducing conditions, biostimulation may be an effective option. Some phenoxy acids were marketed in racemic mixtures, and biodegradation rates may differ between enantiomers. Therefore, enantio-preferred degradation of mecoprop (MCPP) in soil was measured to get in-depth information on whether amendment with glucose (BOD equivalents as substrate for microbial growth) and nitrate (redox equivalents for oxidation) can stimulate bioremediation. The degradation processes were studied in soil sampled at different depths (3, 4.5 and 6m) at a Danish urban site with a history of phenoxy acid contamination. We observed preferential degradation of the R-enantiomer only under aerobic conditions in the soil samples from 3- and 6-m depth at environmentally relevant (nM) MCPP concentrations: enantiomer fraction (EF)<0.5. On the other hand, we observed preferential degradation of the S-enantiomer in all samples and treatments at elevated (μM) MCPP concentrations: EF>0.5. Three different microbial communities were discriminated by enantioselective degradation of MCPP: 1) aerobic microorganisms with little enantioselectivity, 2) aerobic microorganisms with R-selectivity and 3) anaerobic denitrifying organisms with S-selectivity.Glucose-amendment did not enhance MCPP degradation, while nitrate amendment enhanced the degradation of high concentrations of the herbicide.

Fate of Point‐Source Pesticide Spill in Clayey Till after 15 Years

AbstractThis study investigated the development of pesticide pollution two, three, and 17 years after spills of the herbicides dichlorprop, mecoprop (MCPP), MCPA, 2,4‐D (phenoxy acids), simazine, and terbutylazine (triazines) in a former orchard machinery service yard. The spills had occurred over several decades on a 23‐m thick, mainly anaerobic fractured clayey till aquitard. Angled monitoring wells were installed in the aquitard 3 years after the spills ceased in 1989. In 1993, monitoring revealed that high groundwater concentrations of dichlorprop (677 µg/L) and MCPP (139 µg/L) were accumulated as a zone of maximum pollution in anaerobic and largely immobile pore water at 5 to 6 m depth in the aquitard profile. In contrast, 2,4‐D was determined in only one water sample, and MCPA and simazine and terbutylazine were determined only in low concentrations (below10 µg/L), although these pesticides had been handled at the site in greater amounts than dichlorprop and MCPP according to detailed historic information obtained for the site. Repeated monitoring in the same wells after a further 14 years in 2007 revealed that no identifiable degradation of MCPP had occurred, while dichlorprop had degraded by 75% to 80% (estimated half‐life of approximately 5 years). Furthermore, degradation products related to the phenoxy acids had accumulated, especially 4‐CPP with a maximum concentration of 218 µg/L. In the same zone, MCPA and simazine had almost disappeared. As the pollution was mainly accumulated in largely immobile pore water of the aquitard clayey matrix, and the groundwater recharge was low (30 to 60 mm/year), only minor vertical displacement of the zone with maximum pollution zone had occurred during the 15 years of monitoring. However, concentrations of dichlorprop (0.01 to 0.02 µg/L), MCPP (0.1 to 0.2 µg/L), and 4‐CPP (0.6 to 0.7 µg/L) had spread along textural heterogeneities in the aquitard into the underlying sandy aquifer at 23‐m depth.

Removal of Herbicide Mecoprop from Surface Water Using Advanced Oxidation Processes (AOPS)

In the last twenty years, due to a number of natural and anthropogenic reasons, many water sources have become poorer in quality with respect to micropollutants. An example of a micropollutant that needs to be removed is the chlorophenoxypropionic herbicide mecoprop (MCPP). MCPP is one of the nine pesticides used as an indicator to monitor pesticide concentrations in rivers because it is frequently found to exceed the 0.1 µg L-1 limit in England and Wales. The aim of this study was to investigate the effectiveness of different AOPs for the degradation of the herbicide Mecoprop (MCPP) in both deionised water (DW) and in surface water using different UV254 intensities and concentrations of reagents. For an initial MCPP concentration of 10 mg L-1, Photo-Fenton at natural pH using 20 mg L-1 of H2O2 and 20 mg L-1 Fe2+ proved to be the most effective process in terms of degradation rate in both DW and surface water. When using an environmentally relevant concentration (1 µg L-1) and natural pH, if optimized, Photo-Fenton and UV/H2O2 processes achieved the best degradation results.

Mecoprop (MCPP) removal in full-scale rapid sand filters at a groundwater-based waterworks

Contamination by the herbicide mecoprop (MCPP) was detected in groundwater abstraction wells at Kerteminde Waterworks in concentrations up to 0.08μg/L. MCPP was removed to below detection limit in a simple treatment line where anaerobic groundwater was aerated and subsequently filtered by primary and secondary rapid sand filters. Water quality parameters were measured throughout the waterworks, and they behaved as designed for. MCPP was removed in secondary rapid sand filters — removal was the greatest in the sand filters in the filter line with the highest contact time (63min). In these secondary sand filters, MCPP concentration decreased from 0.037μg/L to below the detection limit of 0.01μg/L. MCPP was removed continuously at different filter depths (0.80m).Additionally, biodegradation, mineralisation and adsorption were investigated in the laboratory in order to elucidate removal mechanisms in the full-scale system. Therefore, microcosms were set up with filter sand, water and 14C-labelled MCPP at an initial concentration of 0.2μg/L. After 24h, 79–86% of the initial concentration of MCPP was removed. Sorption removed 11–15%, while the remaining part was removed by microbial processes, leading to a complete mineralisation of 13–18%. Microbial removal in the filter sand was similar at different depths of the rapid sand filter, while the amount of MCPP which adsorbed to the filter sand after 48h decreased with depth from 21% of the initial MCPP in the top layer to 7% in the bottom layer.It was concluded that MCPP was removed in secondary rapid sand filters at Kerteminde Waterworks, to which both adsorption and microbial degradation contributed.

Effect of Mecoprop (RS)-MCPP on the biological treatment of synthetic wastewater in an anaerobic membrane bioreactor

The effects of Mecoprop (RS)-MCPP were investigated in an anaerobic membrane bioreactor (AnMBr) fed with synthetic wastewater containing stepwise increases in Mecoprop concentration, 5–200mgL−1 over 240days. Effects were observed in terms of soluble chemical oxygen demand (COD) removal efficiency, volatile fatty acid (VFA) production, and methane yield. Soluble COD removal efficiency was stable at Mecoprop concentrations below 200 (±3)mgL−1, with an average of 98 (±0.7)% removal. However, at 200 (±3)mgL−1 Mecoprop, the COD removal efficiency decreased gradually to 94 (±1.5)%. At 5mgL−1 Mecoprop, acetic and propionic acid concentrations increased by 60% and 160%, respectively. In contrast, when Mecoprop was increased to 200 (±3)mgL−1, the formation and degradation of acetate was unaffected by the higher Mecoprop concentration, acetate remaining below 35mgL−1. Increases in the Mecoprop specific utilization rate were observed as Mecoprop was increased stepwise between 5 and 200mgL−1.

Assessment of the contamination of drinking water supply wells by pesticides from surface water resources using a finite element reactive transport model and global sensitivity analysis techniques

► Surface water contaminants can reach water wells located in confined aquifers. ► Global sensitivity analysis tools allowed identifying most important parameters. ► Well depth, pesticide characteristics and clay layer thickness are very important. ► Persistent compounds in surface water can pose a threat to drinking water supply wells. A reactive transport model is employed to evaluate the potential for contamination of drinking water wells by surface water pollution. The model considers various geologic settings, includes sorption and degradation processes and is tested by comparison with data from a tracer experiment where fluorescein dye injected in a river is monitored at nearby drinking water wells. Three compounds were considered: an older pesticide MCPP (Mecoprop) which is mobile and relatively persistent, glyphosate (Roundup), a newer biodegradable and strongly sorbing pesticide, and its degradation product AMPA. Global sensitivity analysis using the Morris method is employed to identify the dominant model parameters. Results show that the characteristics of clay aquitards (degree of fracturing and thickness), pollutant properties and well depths are crucial factors when evaluating the risk of drinking water well contamination from surface water. This study suggests that it is unlikely that glyphosate in streams can pose a threat to drinking water wells, while MCPP in surface water can represent a risk: MCPP concentration at the drinking water well can be up to 7% of surface water concentration in confined aquifers and up to 10% in unconfined aquifers. Thus, the presence of confining clay aquitards may not prevent contamination of drinking water wells by persistent compounds in surface water. Results are consistent with data on pesticide occurrence in Denmark where pesticides are found at higher concentrations at shallow depths and close to streams.

Comparison of concentrations and stereoisomer ratios of mecoprop, dichlorprop and metolachlor in Ontario streams, 2006–2007 vs. 2003–2004

Mecoprop, dichlorprop and metolachlor concentrations and enantiomer signatures were determined in Ontario streams in 2006–2007 and compared to results from 2003 to 2004. Median concentrations of dichlorprop and metolachlor were not significantly different between the two campaigns, but mecoprop was higher in 2006–2007. Concentrations of mecoprop and dichlorprop in Lake Ontario surface water were 1–2 orders of magnitude lower than stream averages. Enantiomer fractions (EFs) > 0.5 of mecoprop in high-concentration stream water samples during 2006–2007 were related to replacement of racemic mecoprop by single (+) enantiomer mecoprop-P after 2004. EFs <0.5 in low-concentration samples suggested enantioselective degradation and/or interconversion. Metolachlor profiles were expressed as SF, the fraction of herbicidally active/(active + inactive) stereoisomers. Samples with higher concentrations of metolachlor had SFs similar to S-metolachlor which is enriched in the active stereoisomers. Low concentrations were associated with lower and more variable SFs, suggesting mixed input of racemic and S-metolachlor or stereoselective degradation.

Chiral Current-Use Herbicides in Ontario Streams

Concentrations of mecoprop, dichlorprop, and metolachlor were investigated in 393 samples from Ontario streams in 2003-2004. Maximum concentrations of mecoprop, dichlorprop, and metolachlor were 1900, 6.62, and 1560 ng L(-1), respectively in 2003, and 103,000, 110, and 5290 ng L(-1), respectively, in 2004. Concentrations of metolachlor in agricultural watersheds were significantly (p < 0.0001) higher than those in urban watersheds, whereas concentrations of mecoprop did not differ (p > 0.1) between the two watershed types. Enantiomer fractions (EFs) of the acid herbicide mecoprop ranged from 0.236 to 0.928 and for dichlorprop EFs ranged from 0.152 to 0.549. EFs of mecoprop did not differ significantly (p > 0.1) between agricultural and urban land usage. Mecoprop EFs > or = 0.5 were found in 54% of samples, a situation expected during the transition years when racemic mecoprop was replaced by mecoprop-P, consisting of only the R(+) enantiomer. However, EFs < 0.5 were found in 46% of samples, which suggests preferential degradation of R(+) or conversion of R(+) to S(-). The four stereopluisomers of metolachlor were separated by HPLC and are reported as the ratio of the two herbicidally active stereoisomers (aS,1'S and aR,1'S) to the two inactive stereoisomers (aS,1'R and aR,1'R). The average S/R of metolachlor in streams was 6.73 +/- 2.28 and ranged from 1.08 to 12.7. Samples with higher concentrations of metolachlor had S/R ratios similar to the S/R of S-metolachlor (enriched in aS,1'S and aR,1'S stereoisomers) whereas samples with lower concentrations display lower S/R ratios with greater variability, suggesting mixed input of racemic and S-metolachlor or stereoselective degradation. S/R values were significantly higher (p < 0.001) in agricultural than urban watersheds. Streamwater from row crop areas showed higher S/R ratios than streamwater from fruit growing areas (p = 0.036).

Comparative depollution of mecoprop aqueous solutions by electrochemical incineration using BDD and PbO2 as high oxidation power anodes

The oxidation ability of the two most used high oxidation power anodes (i.e., anodes with high overpotential for O2 evolution), lead dioxide (PbO2) and boron-doped diamond (BDD), has been compared for the electrochemical incineration of solutions containing the herbicide mecoprop (MCPP) by using an electrolytic flow cell. The influence of several operating parameters such as current, liquid flow rate and MCPP concentration on the performance of both systems with a stainless steel cathode has been studied. Galvanostatic electrolyses always lead to complete mineralization due to the high amounts of effective hydroxyl radicals generated from water oxidation at each anode. The current efficiency using PbO2 is low, thus yielding extremely high energy consumption, while BDD anode exhibits faster oxidation rate and greater current efficiencies, along with a significantly lower energy cost. In this system MCPP disappears at a time similar to that required for overall mineralization, following a pseudo first-order kinetics that is typical of a constant excess of oxidizing hydroxyl radical. GC–MS analyses reveal that the electrochemical degradation pathway involves the same aromatic and carboxylic acid intermediates when using PbO2 or BDD anodes and that oxalic acid is the ultimate by-product prior to conversion to CO2.

Effect of nutrient amendments and sterilization on mineralization and/or biodegradation of 14C-labeled MCPP by soil bacteria under aerobic conditions

Mineralization and/or degradation of the phenoxy herbicide mecoprop (MCPP) by a group of soil bacteria under the effects of nutrient amendments and sterilization were investigated. Five different species of Pseudomonas ( P. paucimobilis , P. aeruginosa , P. mallei , P. pseudomallei , and P. pickettii ) were isolated from sediments of Lake Mariut, a freshwater lake in south Alexandria, Egypt. MCPP mineralization and/or removal were tested by the selected Pseudomonas species as active and dead masses in minimal and nutrient-rich media supplemented with 14 C-MCPP at a final concentration of 10 μg l −1 for 6 successive weeks. Results revealed significant variations in the removal percentages of MCPP by either mineralization or biodegradation. Pseudomonas spp. exhibited high selectivity toward MCPP. Considering the short duration of the experiment (45 days) Pseudomonas spp. investigated in this study provide an effective and selective potential for MCPP decontamination. As a general trend, all of the investigated species exhibited higher biodegradation and removal efficiency of MCPP (1.3–89.5%) compared to their mineralization abilities (0.10–9.28%) under the experimental conditions. Also the highest MCPP mineralization and degradation by the selected Pseudomonas spp. were achieved by their inactive (dead) followed by active-rich cultures (both were inoculated in nutrient-rich medium), confirming the positive effects of nutrient amendments and sterilization on MCPP decontamination. Efficiency of Pseudomonas spp. was positively correlated with time up to the 3rd week for biodegradation and up to the 6th week for mineralization, indicating high mineralization efficiency provided enough time. Finally, Pseudomonas spp. showed selective preferences among them toward MCPP with the highest mineralization efficiency achieved by P. aeruginosa (1SB) and P. mallei (2SA), while the highest biodegradation efficiency was achieved by P. pickettii (5SB) and P. pseudomallei (3S). They seemed very promising but require longer exposure and higher MCPP concentration to stimulate and enhance their metabolic and mineralization capabilities. Results of this study can be manipulated efficiently to select the most promising Pseudomonas species for decontaminating polluted systems providing the optimum degradation conditions.

Effect of herbicide concentration and organic and inorganic nutrient amendment on the mineralization of mecoprop, 2,4-D and 2,4,5-T in soil and aquifer samples

The impact of the herbicide concentration (0.10–10 000 μg kg −1) and addition of organic and inorganic nutrients on mecoprop, 2,4-D and 2,4,5-T mineralization in aquifer and soil samples was studied in laboratory experiments. Generally, 2,4-D was most rapidly mineralized followed by mecoprop and 2,4,5-T. A shift from non-growth to growth-linked mineralization kinetics was observed in aquifer sediment with 2,4-D concentrations >0.10 μg kg −1 and mecoprop concentrations >10.0 μg kg −1. The shift was apparent at higher herbicide concentrations in soil coinciding with a lower bioavailable fraction and a higher herbicide sorption to soil. Herbicide addition did not affect the bacterial density, although 2,4-D and mecoprop applied at 10 000 μg kg −1 stimulated growth of specific degraders. Generally, nutrient amendments did not stimulate mineralization at the lowest herbicide concentrations. In contrast, the mineralization rate of higher herbicide concentrations was significantly stimulated by the amendment of inorganic nutrients.

Linking a one-dimensional pesticide fate model to a three-dimensional groundwater model to simulate pollution risks of shallow and deep groundwater underlying fractured till

The one-dimensional pesticide fate model MACRO was loose-linked to the three-dimensional discrete fracture/matrix diffusion model FRAC3DVS to describe transport of the pesticide mecoprop in a fractured moraine till and local sand aquifer (5–5.5 m depth) overlying a regional limestone aquifer (16 m depth) at Havdrup, Denmark. Alternative approaches to describe the upper boundary in the groundwater model were examined. Field-scale simulations were run to compare a uniform upper boundary condition with a spatially variable upper boundary derived from Monte-Carlo simulations with MACRO. Plot-scale simulations were run to investigate the influence of the temporal resolution of the upper boundary conditions for fluxes in the groundwater model and the effects of different assumptions concerning the macropore/fracture connectivity between the two models. The influence of within-field variability of leaching on simulated mecoprop concentrations in the local aquifer was relatively small. A fully transient simulation with FRAC3DVS gave 20 times larger leaching to the regional aquifer compared to the case with steady-state water flow, assuming full connectivity with respect to macropores/fractures across the boundary between the two models. For fully transient simulations ‘disconnecting’ the macropores/fractures at the interface between the two models reduced leaching by a factor 24. A fully connected, transient simulation with FRAC3DVS, with spatially uniform upper boundary fluxes derived from a MACRO simulation with ‘effective’ parameters is therefore recommended for assessing leaching risks to the regional aquifer, at this, and similar sites.

Pesticide pollution of the Triassic Sandstone aquifer of South Yorkshire

Diffuse pollutants such as pesticides pose a significant threat to groundwater quality. Following the wet autumn and winter of 2000–2001 an upturn in trace pesticide concentrations was detected in blended water drawn from part of the Triassic Sandstone aquifer. A groundwater sampling and monitoring programme was undertaken to assess whether this increase would continue. Over a period of 18 months, 190 groundwater samples were collected from the upper part of the aquifer and analysed for 40 pesticides and for nitrate. A total of 25 pesticides were found of which 16 were detected more than once. Positive pesticide detections were in excess of the EU maximum admissible concentration (MAC) for individual substances of 0.1 μg l −1 on 33% of occasions. The most commonly detected pesticides generally have higher agricultural application rates and/or relatively greater solubilities. Very high concentrations of mecoprop (up to 7.1 μg l −1 ) were consistently found at two of the sampling sites. Analysis of mecoprop enantiomers suggested more than one source for this contaminant. High concentrations of atrazine (up to 1.4 μg l −1 ) were also detected at three sites and high concentrations of isoproturon (1.2 μg l −1 ) were found where very high mecoprop concentrations were also present. Nitrate concentrations exceed the EU MAC of 11.3 mg l −1 N at four sites. The spatial and temporal distribution of pesticides obtained from the monitoring network shows no clear trends for prediction of future concentrations. Nitrate-N concentrations and pesticide detections show no clear relationship, suggesting different source, transport or degradation pathways.

Aquifer Vulnerability to Pesticide Migration Through Till Aquitards

This study investigates the influence of key factors-mainly recharge rate and degradation half-life--on downward migration of the widely used pesticide mecoprop (MCPP) through a typical clayey till aquitard. The study uses the numerical model FRAC3Dvs, which is a three-dimensional discrete fracture/matrix diffusion (DFMD) numerical transport model. The model was calibrated with laboratory and field data from a site near Havdrup, Denmark, but the overall findings are expected to be relevant to many other sites in similar settings. Fracture flow and MCPP transport parameters for the model were obtained through calibration using well-characterized laboratory experiments with large (0.5 m diameter by 0.5 m high) undisturbed columns of the fractured till and a field experiment. A second level of upscaling and sensitivity analysis was then carried out using data on hydraulic head, fracture spacing, and water budget from the field site. The simulations of downward migration of MCPP show that MCPP concentration and mass flux into the underlying aquifer, and hence the aquifer vulnerability to this pesticide compound, is mainly dependent on the degradation rate of the pesticide, the overall aquitard water budget, and the ground water recharge rate into the aquifer. The influence of flow rate, matrix diffusion, and degradation rate are intertwined. This results in one to four orders of magnitude higher MCPP flux into the aquifer from aquifer recharge rates of 20 and 120 mm/yr, respectively, for no degradation and MCPP half-life of 0.5 yr. From a sensitivity analysis it was found that the range of MCPP flux into the aquifer varied less than one order of magnitude due to (1) changing fracture spacing from 1 to 10 m, or (2) preferential flow along inclined thin sand layers, which represent common conditions for the current and other settings of clayey till in Denmark and other glaciated areas in Europe and North America. The results indicate that for aquifers overlain by fractured clayey tills, the vulnerability to contamination with pesticides (pesticide flux into the aquifer) and other widespread agricultural contaminants is going to vary strongly in the watershed as a function of the distribution of aquitard water budget (flow rate) and aquitard redox environment (controlling contaminant degradation rates), even if the thickness of the till is relatively constant. DFMD modeling of cause-effect relationships within such systems has great potential to support decisions in planning, regulation, and contaminant remediation.

Transport of mecoprop from agricultural soils to an adjacent salt marsh

Salt marshes are important ecological areas and play a significant role in coastal flood defence schemes. In many areas of the UK they are adjacent to agricultural areas utilised for the growth of cereal crops, for which mecoprop is used as a selective herbicide in the control of broad-leafed weeds. This study measured concentrations of mecoprop in soils, drainage ditch waters and sediments and salt marsh sediments over a period of 138 days following spring application. Soil concentrations of up to 1827 μg/g were recorded after application, which demonstrated a half life for mecoprop of from 9 to 12 days, with first order kinetics. However, a major rainfall event 9 days after application resulted in significant transport of herbicide to the salt marsh via subsurface field drains, drainage ditches and discharge sluice. Mecoprop concentrations of up to 386 μg/l observed in water samples were above UK guidelines.

RUNOFF FROM FESCUE PLOTS TREATED WITH TRIMEC

Runoff of herbicides can promote adverse impacts in receiving waters. The objective of this study was toassess the effects of rainfall delay, herbicide application rate, rainfall intensity, and pre-application rainfall on runoff ofTRIMEC (a combination of 2,4-D, dicamba, and mecoprop), a herbicide that is commonly used in central Kentucky. Thelevels of rainfall delay were 0, 2, and 4 d following application; and the levels of herbicide application rate were 0, 0.5,1 and 2 times the recommended rate. Simulated rainfall was applied at intensities of 64, 102, and 140 mm h1; and thedepths of water applied prior to TRIMEC application were 0, 13, and 25 mm. Flow-weighted composite runoff sampleswere analyzed by gas chromatography. Maximum concentrations in runoff for treatment combinations studied were:2,4-D, 45.5 g L1; dicamba, 1.59 g L1; and mecoprop, 212 g L1. The rainfall delay affected both 2,4-D anddicamba concentrations but not mecoprop concentration, suggesting that its foliar half-life might be longer thansuggested. As anticipated, runoff concentrations of all TRIMEC constituents were significantly (p < 0.05) affected byherbicide application rate. Rainfall intensity affected only the concentration of mecoprop, with concentrations at thehighest intensity being significantly (p < 0.05) greater than those at the two lower concentrations. Pre-applicationrainfall had no significant effects on runoff concentrations. Mass transport averaged 1.51, 0.38, and 14.8% of amountsapplied for 2,4-D, dicamba, and mecoprop, respectively, reflecting differences in degradation rates, wash-offcharacteristics and other factors. Mass transport was in no case significantly affected by the treatments. The findings ofthis study suggest that when TRIMEC is applied at the recommended rate under comparable soil, vegetation and weatherconditions, the potential for 2,4-D to exceed the maximum contaminant level of 70 g L1 in runoff is low.

Occurrence of the Pharmaceutical Drug Clofibric Acid and the Herbicide Mecoprop in Various Swiss Lakes and in the North Sea

Clofibric acid (CA) and the herbicide mecoprop (MCPP) were detected in Swiss lakes from populated areas and in the North Sea in the low nanograms per liter range. Gas chromatography/mass spectrometry (GC/MS) and MS/MS were used to distinguish the two isomeric compounds (analyzed as the methyl esters). The concentrations of CA in the North Sea (1−2 ng/L) reach levels of those of “classical” environmental pollutants such as α- and γ-hexachlorocyclohexane. The data suggest a high mobility of CA in the aquatic environment. The changed relative concentrations of CA and MCPP in the North Sea as compared to those in the lakes and in comparison to produc tion figures indicate a much more persistent behavior for CA than for MCPP. The data also indicate that some pharmaceutical compounds need evaluation on ecotoxicological grounds in very much the same way as do agricultural chemicals.

Agricultural inputs of mecoprop to a salt marsh system: Its fate and distribution within the sediment profile

The mass of mecoprop discharged in agricultural drainage waters directly onto a salt marsh has been determined and the subsequent fate and distribution of mecoprop within the vegetated and mud flat sediments investigated. The results show the leaching of high mecoprop concentrations from the agricultural soils following heavy rain, with peak concentrations in drainage waters preceding peak water discharges. A direct increase in mecoprop concentration within salt marsh sediments was also identified and, consequently, a preliminary evaluation of the potential threat of the mecoprop loadings to the indigenous biota of the dynamic salt marsh system was made.

Movement of pesticides to surface waters from a heavy clay soil

AbstractA field experiment at Cockle Park, Northumberland on a clay loam soil (Dunkeswick series) cropped with winter wheat investigated the effects of drainage and season of application on pesticide movement. Isoproturon, mecoprop, fonofos and trifluralin were applied in two consecutive seasons at normal agricultural rates to three hydrologically isolated plots each of 0.25 ha. Two of the plots were mole‐drained and the third was an undrained control. Surfacelayer flow and drainflow from each plot were monitored at 10‐min intervals. Samples of flow were analysed for pesticides to evaluate transport of applied chemicals from the site. Despite widely differing properties (Koc 20–8000 ml g−1, t1/2 10–60 days), all four pesticides were found in surface‐layer flow and mole drainflow from the site. Maximum concentrations of pesticides in flow ranged from 0.1 to 121 μg litre−1 (aqueous phase) and &lt; 0.2 to 48 μg litre−1 (particulate phase). Over two contrasting seasons, total losses of pesticides in flow followed total amounts of flow and were approximately four and five times larger, respectively, in 1990/91 than in 1989/90. The maximum loss occurred from the undrained plot and was 2.8 g isoproturon (0.45% of that applied). Total losses of autumn‐applied pesticides from an undrained plot were up to four times greater than losses from a mole‐drained plot. Mole drainage decreased movement of pesticides from this slowly permeable soil by reducing the amount of surfacelayer flow. Maximum concentrations of mecoprop and isoproturon in drainflow were 10–20 times larger following spring application than after application in autumn. Bypass flow down soil cracks was an important process by which pesticide was lost from the site, with transport to the drainage system via mole channels (55 cm depth) after less than 0.5 and 6.7 mm net drainage in the two winters.