Issue Date: August 11, 2014 | Web Date: August 8, 2014
Danger From Microcystins In Toledo Water Unclear
An academic lab on Aug. 7 released test results of water from Lake Erie that paint a more complicated, and possibly less toxic, picture of the potential health hazards from the presence of algal toxins in the tap water of Toledo, Ohio. Residents were ordered not to drink from their taps for several days.
On Aug. 1, the Collins Park Water Treatment Plant, which treats Toledo’s Lake Erie-based water supply, found elevated levels of microcystins, a class of more than 90 related compounds that are produced by blue-green algae, or cyanobacteria, and which are highly toxic to the livers of humans and other animals.
The situation prompted the Ohio Environmental Protection Agency to order the temporary tap water ban, which was lifted on Aug. 4.
But the true danger posed by the microcystin contamination remained unclear because scientists didn’t know exactly which microcystins were present, says Gregory L. Boyer, acting director of the Great Lakes Research Consortium. He notes that algae found in Lake Erie produce different microcystins with varying toxicities.
Without knowing which microcystins were involved, overall levels detected in Toledo tap water “say nothing about toxicity in humans,” Boyer points out.
But now Boyer’s lab—which is independent of government labs—reports that samples taken on Aug. 4 of Lake Erie’s contaminated water contained 60–80% microcystin-LR, 10–25% microcystin-RR, and 5–15% microcystin-YR.
Microcystin-LR is considered to be the most toxic, microcystin-RR is half as toxic as the LR variant, and microcystin-YR is somewhere in between the two.
The World Health Organization’s recommended safe limit of microcystin in water of 1.045 µg per liter is based on the toxicity of microcystin-LR. The new results suggest that the actual toxicity to people in Toledo may have been overestimated.
On Aug. 1, prompted by the presence of a bloom of blue-green algae, the Toledo water facility performed tests that showed elevated mycrocystin levels. Continued daily testing showed levels that exceeded WHO’s recommendations, reaching 2.5 µg/L, according to a statement from the Toledo-Lucas County Health Department. But by Aug. 4, they were below 1.0 µg/L.
The tests use enzyme-linked immunosorbent assays and are not able to differentiate among microcystin variants. Instead, they report the presence of ADDA, an unusual amino acid present in all microcystins.
Other testing techniques, such as reversed-phase HPLC or Raman spectroscopy can separate different microcystins, but they are time and labor intensive. Boyer’s lab relied on an LC/MS screening method.
Microcystins are difficult to remove from water. They are cyclic peptides, which are stable even at high temperatures. Microcystins are even impervious to enzymatic degradation, Boyer says, because they contain unusual linkages that normal enzymes don’t recognize.
The recent contamination was mitigated by a number of factors, says Ohio EPA spokeswoman Heidi Griesmer. Weather conditions helped dilute the toxins, and the treatment facility added extra powdered activated carbon, alum, and chlorine to the water supply, she says.
The carbon powder readily adsorbs microcystins; alum causes any remaining algae to clump together and settle out of the water; and chlorine, along with sunlight, can oxidize an unsaturated double bond in ADDA, leading to chemical breakdown of the toxins.
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