An examination of environmentally safe levels of zinc (II), cadmium (II) and lead (II) with reference to impact on channelfish Nuria denricus

As a continuation of our earlier studies on the impact of heavy metals on aquatic organisms (Abbasi & Soni, 1984), the behavioural responses and survival of the teleost Nuria denricus exposed to different levels of zinc (II), cadmium (II) and lead (II) were studied. Safe concentration (SC) values of the metals were determined with the help of computer-aided long-term bioassays.

Comparisons of the SC with the minimum allowable levels of the corresponding metals in drinking water, effluents, irrigation water and fisheries revealed that, except for a few cases, the existing national and international water quality standards for various water uses are higher than the SC. The disparity between the SC and the permitted levels of zinc and cadmium was especially noteworthy, indicating the need for a thorough re-evaluation of the toxicity and safe levels of these metals.