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Drought Changes Toxicity Of Aquatic Pollutants

US - Some areas of the southern US are suffering from the longest dry spell since 1887. That could prove problematic for aquatic organisms, according to a study from Baylor University.

The research found that drought conditions make some chemicals in the environment more toxic to fish and other aquatic life. Specifically, drought conditions were found to exacerbate the magnitudes of natural pH shifts in the water. This is important, the researchers say, because the toxicity to aquatic life of some contaminants, such as ammonia, depends on the pH level.

Also, more than 75 per cent of the essential drugs described by the World Health Organisation and approximately one-third of modern pesticides have ionizable groups of compounds. These "weak base" compounds can become more toxic to fish when dispersed in the environment if surface pH levels are high.

The findings appear on-line in the journal Integrated Environmental Assessment and Management.

"The importance of this work is it shows that we may be underestimating or overestimating the adverse effects of some chemicals on fish," says study co-author Bryan Brooks of Baylor University.

"How drought conditions, especially those influenced by climatic changes, impact fluctuations of the water's pH level is just now emerging as an area of concern in regards to making certain chemicals more toxic and more likely to accumulate in fish."

The Baylor researchers took samples at different times over the course of two years at 23 streams across the southern US. They measured how ecosystem production and respiration, dissolved oxygen content, the amount of phosphorus and nitrogen, and pH level changed over the course of a day.

In the year that was one of the driest on record, the fluctuations of the water's pH level were extreme and coincided with increased toxicity to aquatic life.

"Future water scarcity associated with global climate change and altered precipitation patterns may profoundly impact in-stream flows in semi-arid regions, which have direct implications for water-resource management," said co-author Ted Valenti, a former Baylor doctoral student.

"Predicting the cumulative effects of climatic variability on the risk of contaminants may require a significant shift in the environmental assessment and management approaches for freshwater systems."

the Fish Site Editor

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