Histological effects of low atrazine concentration on zebra mussel (Dreissena polymorpha Pallas)

The s-triazine herbicide atrazine (2-chloro-4-ethylamino-6-isopropyl-amino-s-triazine) is one of the most used pesticides in the world. The greatest quantity of atrazine is used for weed control in corn, sorghum, sugarcane and other crops. It is one of the most frequently detected pesticides in surface- and ground waters in Europe and North America due to its widespread use, low chemical reactivity, relative mobility and high persistence in the environment. The highest concentrations were detected in streams and rivers in agricultural regions, after applications in spring and early summer. Such frequent appearance of atrazine in natural waters has generated a lot of research into its toxicity in aquatic systems, especially on green alga and macrophita. The effects of atrazine in environmentally realistic concentrations on freshwater animals are less studied. The best known are the effects on fishes. The concentrations of 1.5, 3.0 and 6.0 mg/L of atrazine inhibit biochemical activity of alkaline phosphatase in carp liver, kidneys and heart. In higher concentrations atrazine caused vacuolisation of hepatocytes with fibrosis and necrosis of surrounding tissues. Gill damages were also noted. Depending on the concentration, atrazine induced progressive degradation of kidney tubular and intertubular tissue and interferes with electrolyte balance in fishes. The concentration of 0.1 mg/L of atrazine during 10 days causes significant irreversible lysis of kidney cells in the snail Physa acuta. In environmentally realistic concentrations it also affects biochemical processes in the freshwater snail Lymnaea palustris, while in Physa acuta and Ancylus fluviatilis, it causes changes in feeding behaviour. It is known that environmentally realistic concentrations of atrazine have negative impact on feeding, growth and egg production in freshwater molluscs, cladoceran and leeches.