Algae Produce An Industrial Contaminant

A common green algae produces selenocyanate, a contaminant that scientists previously thought entered the environment solely through industrial discharges, according to new research in Environmental Science & Technology (DOI: 10.1021/es103337p).

Selenium is an essential trace mineral for humans and animals, but it becomes toxic at high doses. It travels through food chains and can bioaccumulate in higher organisms, says study co-author Denina Simmons of the government agency Environment Canada. The bioconcentration of selenium can result in birth defects and other reproductive problems in egg-laying vertebrates, such as fish and waterfowl.

Some types of algae can transform inorganic forms of selenium in the environment, such as selenate (SeO₄^2–), into more-bioavailable organic forms, such as selenomethionine. Researchers have mainly studied algae by exposing them to unnaturally high concentrations of selenium in the laboratory. Simmons and Dirk Wallschläger, an environmental chemist at Trent University, Peterborough, Ontario, exposed a ubiquitous freshwater green algae, Chlorella vulgaris, to environmentally relevant concentrations of selenate to observe how the organisms took up and transformed the chemical. The algae's ability to take up the selenate was no surprise, but the researchers discovered something unexpected when the algae began to grow exponentially: The concentrations of two inorganic compounds, selenite (SeO₃^2-) and selenocyanate (SeCN^-)—as identified by ion chromatography coupled to inductively coupled plasma mass spectrometry—began to rise.

Previously, the only known sources of selenocyanate were industrial sources such as petroleum refineries and gold and silver mines. As a result, regulators had considered using the compound for tracing selenium emissions from such industrial activities, Wallschläger says. But the new study suggests that, because selenocyanate also may be produced biotically in the environment, it would not be suitable as a tracer of its industrial sources, he says.

Simmons notes that algae's production of selenocyanate could have ramifications for organisms higher on the food chain. This spring, Wallschläger plans to sample freshwater sites where selenate is present to see if Chlorella vulgaris—and perhaps other species of algae—also produce selenocyanate under environmental conditions.