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Long-term toxicity to fish

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The lowest concentration of un-ionised ammonia at which long-term effects were found is 0.022 mg/L (NH3) when a cumulative mortality of 71 per cent was observed for eggs, larvae and fry of rainbow trout (Oncorhynchus mykiss) over 73 days exposure. No NOEC value was derived in the study since effects were observed at the lowest exposure concentration. However, data on the concentration–response curve for similar effects in other fish have been evaluated, and these indicate 2–3 times difference in exposure concentration for a 50 per cent reduction in survival (from the controls) in such an early life stage test

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Pink salmon (Oncorhynchus gorbuscha) alevins were exposed to concentrations of unionized ammonia ranging between 0 and 4 mg/L (Rice & Bailey, 1980). The highest exposure concentration of ammonia caused significant decreases in weight of exposed fry in all three exposure groups. At 2.4 mg/L un-ionized ammonia, the groups held for 40 days and 61 days were significantly smaller in length and weight and at 1.2 mg/L un-ionized ammonia there was no significant difference. The NOEC was therefore concluded to be 1.2 mg/L un-ionised NH3. Effects were consistently more adverse for groups held 61 days.

Juvenile channel catfish (L. punctatus) were exposed to 12 ammonia concentrations ranging from 48-2048 mg un-ionized NH3-N/L for 31 days (Colt & Tchobanoglous, 1978). On a wet weight basis, growth was reduced by 50% at 517 ug/L un-ionized NH3-N and no growth occurred at 967 ug/L un-ionized NH3-N and higher. Above 500 ug/L un-ionized NH3-N, there was increasing damage to the dorsal and pectoral fins.  The overall NOEC for the growth and weight was < 48 ug un-ionized NH3-N/L.

Fertilised rainbow trout eggs were exposed to 0.05, 0.10, 0.19, 0.28, and 0.37 mg NH3-N/L for periods of either 25 or 33 days followed by 42 days post hatch observations. Egg mortality was not affected in either run by any of the ammonia concentrations. Growth and development of rainbow trout sac fry are inhibited by long-term exposures to concentrations of ammonia as low as 0.05 mg NH3-N/L (Burkalter & Kaya, 1977).

The toxicity of ammonia to early life stages of rainbow trout (Salmo gairdneri) was examined in hard fresh water (Solbe & Shurben, 2003). When exposure began within 24 h of fertilisation and proceeded for 73 days, severe mortality (> 70%) occurred, particularly among the eggs, at concentrations of unionised ammonia as low as 0.027 mg l−1as NH3. When exposure did not start until the eyed-egg stage (c. 24 days) only 40% of the eggs, yolk-sac fry and fry (but especially the fry) died at 0.27 mg l−1as NH3. The authors conclude that both the standards proposed for protecting fish communities and the protocols drawn up for assessing the effects of chemicals should take into account the sensitivity of early life stages of freshwater fish. In particular, in evaluating chemicals, exposure should begin as soon as possible after fertilisation