Water Quality Standards

The acute toxicity of cyanides is high. Cyanides can be found in some foods, particularly in some developing countries, and they are occasionally found in drinking-water, primarily as a consequence of industrial contamination.

Effects on the thyroid and particularly the nervous system were observed in some populations as a consequence of the long-term consumption of inadequately processed cassava containing high levels of cyanide. This problem seems to have decreased significantly in the West African populations in which it was widely reported, following a change in processing and a general improvement in nutritional status.

There are a very limited number of toxicological studies suitable for use in deriving a guideline value. There is, however, some indication in the literature that pigs may be more sensitive than rats. There is only one study available in which a clear effect level was observed, at 1.2 mg/kg of body weight per day, in pigs exposed for 6 months. The effects observed were in behavioural patterns and serum biochemistry.

Using the LOAEL from this study and applying an uncertainty factor of 100 to reflect inter- and intraspecies variation (no additional factor for a LOAEL was considered necessary because of doubts over the biological significance of the observed changes), a TDI of 12 µg/kg of body weight was calculated.

An allocation of 20% of the TDI to drinking-water was made because exposure to cyanide from other sources is normally small and because exposure from water is only intermittent. This results in a guideline value of 0.07 mg/litre (rounded figure), which is considered to be protective for acute and long-term exposure.