ABSTRACT
Following their introduction in the late 1970’s, the synthetic pyrethroid insecticides gained rapid and enormous support from the agricultural community because of their wide spectrum of activity on the pests of numerous crops, relatively low cost, low application rates and safety in use. However, under laboratory conditions in water without particulate matter, these products were shown to have a high toxicity to fish and some aquatic invertebrates. The pyrethroids are of very low water solubility/high lipophilicity, and therefore are rapidly and strongly adsorbed to the particulate material and other surfaces in natural bodies of water. In the adsorbed state their bioavailability to aquatic organisms is greatly reduced and thus, under field conditions, the impact of these insecticides was predicted (prior to their agricultural use) as being much less than suggested by laboratory acute or chronic toxicity test data.
During the past 15 years, approximately 100 freshwater aquatic field tests have been undertaken with pyrethroid insecticides in order to study the potential impact of these products on aquatic organisms, following agronomic, public health and forestry usage. The studies have been carried out in natural/farm ponds, streams or rivers (bifenthrin, cyfluthrin, cypermethrin, deltamethrin, fenvalerate and permethrin), rice paddies (cypermethrin, lambda-cyhalothrin and permethrin), ponds for farming fish and crayfish (fenvalerate and permethrin), lake limnocorral enclosures (fenvalerate and permethrin), pond littoral enclosures (cypermethrin, esfenvalerate and permethrin) and outdoor pond microcosms or mesocosms (bifenthrin, cyfluthrin, cypermethrin, deltamethrin, esfenvalerate, lambda-cyhalothrin, permethrin and tralomethrin).
In this paper it is demonstrated that for the pyrethroids, the system design, size and location has relatively little influence either on the fate of the product in the water column or on the overall impact upon the aquatic organisms, principally due to their rapid loss from the water column by adsorption. The spectrum of biological effects of these products in bodies of water, at application rates equivalent to a single “drift-entry” of 1–5% of the USA labelled maximum use-rate (applied as multiple treatments), is limited to the zooplanktonic and macroinvertebrate crustaceans and to some of the insects. At rates representative of “worst case” expected environmental entry concentrations, the synthetic pyrethroid insecticides used in agriculture all behave very similarly in the aquatic environment. It is likely that these products, when used as recommended in agriculture, will generally have only occasional, minor and transient effects on nearby aquatic ecosystems.
