Mecoprop is an acid herbicide that is widely used for agricultural, horticultural and domestic purposes. It is considered one of the key indicators of pollution from municipal solid waste landfill, as it is frequently identified in landfill leachate. Mecoprop is the most frequently occurring herbicide detected in UK groundwater and the second most common herbicide in UK surface waters. Mecoprop is water-soluble and subject to relatively little retardation by sorption processes, hence it is subject to relatively conservative transport in soils and aquifers. Once in the subsurface it can be persistent. Information and data to underpin the assessment of mecoprop fate and attenuation in the subsurface are therefore of particular importance. This paper reviews the processes that contribute to the attenuation of mecoprop in the subsurface, particularly in groundwater. Biodegradation of mecoprop is the only significant destructive attenuation mechanism operating under subsurface conditions. Biodegradation in topsoil has been relatively widely studied and is commonly observed, but the scientific literature on mecoprop biodegradation in the deeper subsurface is limited and indicates great variability as to the degree and rate at which it takes place, particularly in aerobic aquifers. The apparent recalcitrance under anaerobic conditions means that where it has been disposed of to landfill it is frequently among the most persistent organic compounds in chemically reducing leachate plumes. Mecoprop sorption to sediment surfaces is related to the organic and inorganic geochemistry of mecoprop and the sediment. It is suggested that the generally applied model that uses KOC for predicting sorption of organic solutes may not be appropriate for use with mecoprop.

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