Abstract
The latent toxicity of pesticides to aquatic organisms was assessed using a freshwater shrimp, Paratya compressa improvisa, in water samples collected from several rivers in the Tsukuba district or Takahamairi bay, lake Kasumigaura, from April 1989 to March 1990. The 4-day mortality of the shrimp increased frequently to high levels in the riverwaters, reaching 100% at maximum, from May to August, in the season pesticides were discharged into the aquatic environment. The 7-day mortality of the shrimp also increased to 5060% at maximum in June or August in areas of lake water 500 m distant from the mouths of the three rivers investigated, although it was much lower than that of the river water itself.
The high mortality of the shrimp in the river waters was considered mostly atributable to the effects of pesticides in the rivers, such as fenthion, fenitrothion and BPMC. The quality of the river or lake waters was found to have changed, making the habitat very undesirable for pesticide-sensitive aquatic organisms such as the shrimp during the season of maximum pestichde discharged into environment.
