Contaminant of the Month: More on algal toxins

Aug. 1, 2015

Environmental conditions that cause toxin production are not well understood.

Past Water Technology articles provide overviews of algal blooms and health advisories. This article elaborates with some questions regarding toxicity, analyses, water treatment and regulatory issues. What are algal toxins?

  • Algal toxins are released during some algal blooms that occur in some surface waters during the summer.
  • Environmental conditions that cause toxin production are not well understood.
  • The most common toxin is microcystin, followed by cylindrospermopsin plus several others, infrequently.
  • The U.S. Environmental Protection Agency (EPA) and Health Canada released slightly different drinking water Health Advisories (HAs) on June 17, 2015.
  • The EPA 10-day HA levels are: Microcystin — 0.3 microgram per liter (μg/L) (0.3 parts per billion) for infants and children less than age 6 and 1.6 μg/L for ages 6 and older. Safety factor = 1,000. Cylindrospermopsin — 0.7 μg/L for infants and children less than age 6 and 3 μg/L for ages 6 and older. Safety factor = 300.

Some toxicity anomalies

  • A two-dose, 28-day rat study was chosen as the basis for the microcystin HA. It had an adverse effect on the liver at the 50 μg/L, the lowest dose tested.
  • A 90-day, three-dose mouse study with a 40 μg/L, no adverse effect level previously used by the World Health Organization was not selected.
  • Cylindrospermopsin’s HA values were based on high-dose liver and kidney effects with a no adverse effect level of 30 μg/L from an 11-week study in mice.
  • Several prior studies often showed mice to be more sensitive to microcystin than rats. Was this rat strain hypersensitive? Is it the best animal surrogate for human risk?
  • Other studies indicated that young animals were usually less sensitive than adults.
  • Human data show toxicity, but dose information is limited.

Analytical methods

  • Enzyme-linked immunosorbent assay (ELISA) are broad spectrum methods preferred by the EPA, with reported quantitation limits of about 0.5 to 1 μg/L, with high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) for confirmation.
  • Different commercial ELISA products may produce different results.
  • Cost per analysis for ELISA is about $50 to $100 in the field and about $50 to $150 in a laboratory. HPLC-MS/MS analysis costs about $200 to $350.

Water treatment

  • Conventional drinking water treatment augmented by powdered activated carbon and possibly  potassium permanganate will effectively remove toxins from treated water.
  • The 1.6 μg/L and above HAs will be met easily, but meeting the 0.3 μg/L HA could be difficult in some circumstances.
  • Filtration to remove algal cells prior to disinfection is recommended because cells will lyse and release toxins.
  • Ozone and free chlorine will lyse cells and also react to detoxify the toxins.
  • Potassium permanganate will lyse cells, but there is some debate on relative reactivity to the toxins.
  • Chlorine dioxide;  chloramines (limited); and high-intensity, ultraviolet light will lyse cells but will not react with the toxins.


  • HAs are advice intended to assist states and water suppliers with decisions if a contaminant is detected.
  • HAs are not federal Maximum Contaminant Level (MCL) regulations, but many states will probably adopt them as state regulations or guidelines.
  • Effectively, they are equivalent to Maximum Contaminant Level Goals. MCLs include considerations of treatment availability and costs.
  • They will become de facto regulations produced without the usual due process and external review and comments provided for regulations by the Safe Drinking Water Act.
  • Some ambiguities exist regarding how water suppliers should interpret data exceeding the 0.3 μg/L HA value. Should they wait 10 days to determine if the level is sustained, or notify the public immediately?


  • HAs are valuable for providing operating guidance in the event of contamination by unregulated contaminants.
  • In this case, producing a regulation would have required a longer time than issuing an HA, but the impacts of the HA could be more significant than many regulations.

Dr. Joseph Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the U.S. EPA Drinking Water Standards Division.

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