Pesticide uses and transfers in urbanised catchments.
Monday 06th June 2005
Author: Blanchoud H, Farrugia F, Mouchel JM. (2004)
Chemosphere, 55: 905-913
METHODOLOGY
An assessment was made of the risk associated with urban use of pesticides for surface water quality in urbanised areas, with particular focus on the implications for water intakes used for drinking water. Two half urbanised watersheds were used in this study: the Morbras and the Réveillon rivers (south-eastern Paris). Their catchment areas were judged to be large enough to represent a combination of land uses. Within each catchment, three sampling stations were defined to cover the urbanisation gradient from forested and agricultural areas to densely urbanised areas nearer to Paris.
Urban user groups were identified and information concerning amount of herbicide purchased and used, application periods, application rates and the types of urban soil treated. Householders were surveyed to assess the use of pesticides in gardens. Information was geographically extrapolated using regional GIS. Agricultural uses were also included as a comparison, including application rates and areas treated.
Automatic sampling was used to collect weekly integrated water samples from April to July 1998, during the period when most products are applied. One sample of approximately 20 ml was usually collected every hour during base flow periods, and the sampling rate was increased threefold for higher flow periods. Refrigerated samplers could not be used, so methylene chloride was added to the empty glass bottles to improve sample conservation.
The analytical method used to determine glyphosate residues was not described.
FINDINGS
In urban areas, 5% of the herbicide residues present were glyphosate. From surveys of householders, 7% of the herbicide used was glyphosate.
Glyphosate was extremely difficult to analyse due to its polar nature and the poor yield of commonly used extraction techniques.
Total herbicide input for the catchments was estimated to be around 8 t/yr, of which 50% was due to non-agricultural uses. It was estimated that around 90% of pesticides applied by urban users was made up of herbicides, equivalent to approximately 1.6 t/yr in the study area.
CONCLUSIONS
Glyphosate was present in urban area residues.
A proportion of herbicides found in surface waters can be attributed to urban usage.