In an extensive study of pesticides in a Chalk catchment, twenty pesticides were selected for study; and this paper reports the findings of an eighteen‐month programme of river and rainwater sampling. The results of periodic samples and an intensive river monitoring programme over the duration of a flood event are described.
Both rain and river water within the catchment were found to contain significant numbers of pesticides at varying concentrations. The paper describes the values and temporal variations which were discovered. Higher concentrations and greater numbers of pesticides appeared to be brought down by floods and high river flows; however, even during low flows, some pesticides were persistently found in the river.
WRc are undertaking a long term study of pesticides in the aquatic environment. A study of the pesticides in the rain, river water and groundwater of the Granta catchment in Cambridgeshire is now in its fourth year. Preliminary results are presented and the concentrations of agricultural pesticides in environmental waters are related to the land‐use within the catchment.
The Granta study is incomplete but certain anomalies in pesticide occurrence can be identified. In particular, the triazines are much more prevalent in the groundwaters than their agricultural usage would lead one to expect.
The limited data base gives problems with modelling the contaminant transport in groundwater. The present situation is reviewed and areas of future work necessary to fulfil the modelling needs identified. These areas of study.
The historical land‐use and pesticide usage; the groundwater quality data base; the pesticide transport in the unsaturated zone.
As part of a survey of pesticides in the UK Major Aquifers, which WRc are undertaking on behalf of the National Rivers Authority, a site at Assarts Farm near Mansfield on the Sherwood Sandstone aquifer has been selected for the study of pesticide movement in the unsaturated zone of the sandstone aquifer.
A difficulty in studying pesticide movement in the unsaturated zone is the need to obtain large volumes of water for analysis. WRc, in co-operation with the Soil Survey and Land Research Centre (SSLRC) has tackled this problem by using a modification of the SSLRC standard soil moisture suction sampler. The modified design (Fig. 1), manufactured by SSLRC, is intended to render the installation as chemically inert as possible, so the sampler shell is of stainless steel, tubes and caps of Teflon and the filter element ceramic. No adhesives or resins were used.
At the design stage it was anticipated that each sampler would yield between about 100 ml and 500 ml depending on the soil moisture at the time of sampling. In order to be able to obtain the necessary volume of water (1.71 for three groups of pesticides) needed to analyse pesticides to the required detection limit, a total of twelve samplers in four clusters (Table 1) of three have been installed. It was intended that under optimum conditions each cluster of three samplers, when bulked, would provide sufficient water for one analysis. Under progressively drier conditions, the samples from the clusters may need to be bulked
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