EPA Releases Draft Recreational Water Quality Criteria for Cyanotoxins
January 6, 2017

On December 19, 2016, EPA released a draft document entitled ''Human Health Recreational Ambient Water Quality Criteria and/or Swimming Advisories for Microcystins and Cylindrospermopsin—2016" designed to protect human health from the effects of harmful algae while swimming or during other recreational water activities. This draft criteria document provides recommended concentrations of microcystins and cylindrospermopsin in recreational waters. According to EPA, these draft criteria do not replace the 2012 recreational water quality criteria recommendations for E. coli and Enterococcus. The public comment period for this draft guidance closes on February 17, 2017. This criteria document may be modified in its final form based on comments received during the public comment period.

What Are Cyanotoxins?

Cyanotoxins, such as microcystins and cylindrospermopsin, are produced by naturally-occurring cyanobacteria, formally called blue-green algae (although they are not an algae, they are bacteria). These toxins are produced by numerous cyanobacteria species that occur in all 50 states in the U.S. Cyanobacteria are photosynthetic (use sunlight for energy to live, grow, and reproduce) and in surface water under certain environmental conditions, such as slow-moving water and high input of nutrients, can reproduce excessively leading to blooms. During blooms, cyanotoxins can concentrate in surface water leading to dangerously elevated levels; thus, these blooms are called harmful algal blooms (HABs). HAB exposure has been associated with inflammatory effects, such as gastrointestinal problems, skin irritation, fever, ear irritation, eye irritation, and kidney and liver damage as well as ecological impacts to commercial and recreational fisheries. Cyanotoxins can persist for periods after the blooms, depending on how quickly they degrade, which is influenced by natural conditions, such as sunlight, organic matter, turnover or flushing of the water body, and water temperature.

What Are EPA’s Draft Recommended Concentrations for Cyanotoxins?

EPA’s recommended concentration is 4 micrograms per liter (µg/L) for microcystins and 8 µg/L for cylindrospermopsin in recreational waters. EPA derived these criteria based on the latest peer-reviewed science on the adverse human health effects of cyanotoxins. Stating that there is insufficient data to develop criteria based on inflammatory effects, EPA based the criteria on concentrations of cyanotoxins associated with effects in the liver and kidney observed in laboratory studies with rodents. Using standard ambient water quality criteria guidance for the protection of human health, the recommended criteria were derived based on an upper end (90th percentile) water ingestion rate for children, because children tend to ingest more water during recreational activities than adults.

These criteria are the first federal recommendations for HABs in recreational waters, although many states have adopted guidelines for cyanotoxins and cyanobacteria. State guidelines and action levels for recreational exposure range from 0.8 to 20 µg/L for microcystins and 4 to 20 µg/L for cylindrospermopsin, according to EPA’s draft criteria document. Of these, the state of California has the lowest action levels for microcystins and cylindrospermopsin.

How Will These Criteria Be Applied?

Under Clean Water Act (CWA) 304(a), EPA developed these criteria for states to consider adopting for the protection of human health in recreational waters. States may use these criteria as swimming advisory levels or as water quality standards (or for both). If states use these values as a swimming advisory to protect swimmers at a beach, EPA recommends that recreational water concentrations not exceed these values on any single day. If states adopt these values as water quality standards for CWA section 303(d) purposes, EPA recommends that recreational water concentrations not exceed these values more than 10 percent of days per recreational season up to one year.

Given that HABs have been traditionally associated with poor water quality and high input of nutrients (e.g., phosphorus and nitrogen), exceedance of these criteria, if adopted as water quality standards, could place the focus of exceedances on suspected point sources.

How Can Exponent Help?

Exponent’s interdisciplinary team of scientists has expertise in all aspects of water quality. Our human health scientists have a deep understanding of the derivation of human health water quality standards and the appropriate use of exposure assumptions and toxicity data in deriving water quality criteria. Exponent environmental scientists and engineers have extensive experience in analysis of surface water quality and contaminant transport, both of which are important for evaluating water quality exceedances. Our scientists and engineers have evaluated dispersion and fate of discharges from existing or proposed wastewater outfalls, water quality conditions in existing and proposed waterbodies, basin-wide impacts of nonpoint source runoff, and impacts of natural and man-made hydrologic changes on water quality. In addition, Exponent staff are pioneers in the use of environmental causal analysis, which is a logical, transparent, and objective step-wise approach to evaluate the likelihood of multiple candidate causes contributing to an observed or hypothesized change in a resource, such as an HAB and other water quality issues.


U.S. Environmental Protection Agency (EPA). Human Health Recreational Ambient Water Quality Criteria or Swimming Advisories for Microcystins and Cylindrospermopsin. Draft. EPA Document Number: 822-P-16-002. December 2016.