Report No FR/D0014
The Occurrence of Selected Chemical Pollutants
(Simazine, Lindane and Permethrin) in River Fish
Very few data exist on levels of pesticides in fish from UK waters. Since there are many causes of variability in such measurements a study programme was devised to measure the concentrations of three pesticides in a range of common cyprinid fishes (dace, gudgeon, roach and chub) which covered the main feeding niches within the family. The three pesticides were chosen to be representative of a) water soluble herbicides (Simazine); b) moderately fat soluble, persistent insecticides (Lindane); c) highly fat soluble less persistent insecticides (Permethrin). Samples were taken from three rivers (Ray - Thames NRA, Nadder - Wessex NRA and Stour - Severn Trent NRA) which were known to have been contaminated with the target pesticides. A review of the literature showed that the range of measured Lindane concentrations in fish from pristine to polluted sites varied in an unsystematic way over several orders of magnitude. Data in the literature were so variable that no acceptable concentration in either water or fish could be proposed. Data for Permethrins and Simazine in freshwater fish were much less numerous.
In this study pesticide concentrations found in the muscle and liver tissues of the fish were generally very low making analysis difficult. Concentration differences between species and feeding types were minimal. Lindane concentrations in river Stour fish muscle were generally higher (2-7 µg kg-1) than those of fish from the other two rivers (0.5-3.6 µg kg-1). Permethrin levels in all fish were generally less than 5 µg kg-1. Although many fish in the Stour had unmeasurable levels of Simazine occasional specimens had concentrations of up to 20 µg kg-1 in muscle. Concentrations of Simazine in fish from the Nadder and the Ray were < 2 µg kg-1.
In the present investigation no relationship was found between the fat content of individual fish and their pesticide content. Similarly, only minimal reductions in the variability of pesticide concentrations was obtained by expressing them relative to lipid content. The benefit in surveys of higher concentrations of lipophilic pesticides in liver tissue was more than cancelled out by the difficulties of analysis created by the relatively small size of the organ in small cyprinid fishes. Hence muscle analysis is recommended for survey work.
Levels of other pollutants in rivers can have secondary effects on pesticide levels in fish by changing the relative availability of different food types. If the acceptable levels of the pesticides in the water of a river were to be set at 0.1 µg l-1 it is calculated that the following approximate maximum concentrations of Lindane (122 µg kg-1); Permethrin (0.4 µg kg-1) and Simazine (8 µg kg-1) might result in cyprinid muscle. The lack of understanding of pesticide transport processes in aquatic systems, uptake mechanisms and criticality of different organs in different fish species with regard to pesticides makes the setting of realistic standards for pesticides in freshwaters and fish flesh very difficult at the present time.
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