Sources of Exposure & Risk Factors

Routes of Exposure

man rowing boat through green algal bloom

Boating in a lake with a HAB. Credit: Photo courtesy of Andy Reich.

A harmful algal bloom (HAB) can occur in water bodies around the world and can affect those who use these water bodies for recreation, agricultural, or drinking 1-4. People can be exposed to a HAB or HAB toxins when they swim, wade, or play in or near contaminated water; eat contaminated fish or shellfish; or use contaminated drinking water. The severity of illness and symptoms can vary depending on the type of exposure and the type of HAB toxin.

The main routes of exposure to HAB toxins are 5:

  • Skin contact (through activities like swimming)
  • Inhalation (by breathing in tiny airborne droplets or mist contaminated with HAB toxins)
  • Ingestion (by eating or drinking food or water contaminated with HAB toxins)

 

Anyone who visits a contaminated water body during a HAB event can be exposed through direct contact with the contaminated water. Skin irritation and reactions in humans and animals can vary depending on the length of contact with the contaminated water and the type of HAB toxin present in the water 1,2.

References
  1. Koreivienė J, Anne O, Kasperovičienė J, Burškytė V. Cyanotoxin management and human health risk mitigation in recreational waters.External Environ Monit Assess. 2014;186(7):4443-59.
  2. Van Dolah FM. Marine algal toxins: origins, health effects, and their increased occurrence.External Environ health Perspect. 2000;108(Suppl 1):133.

People can be exposed to a HAB or HAB toxins by inhaling (breathing in) tiny water droplets, mist, or sea spray from a contaminated body of water. This can occur even if a person does not go into the water 1. Further research is needed to better understand the effects of long-term inhalation exposure to HAB toxins, especially for those who regularly work on or near water, such as boaters or lifeguards 1-4.

Individuals who have been on the beach or on a boat during a marine HAB event have reported breathing difficulties after inhaling air or water particles contaminated with HAB toxins 1,5,6. A study conducted during a Florida red tide found that marine HAB toxins could be transported in the air almost 4 miles inland from the water source 7. A marine HAB may cover hundreds of square miles of ocean and affect boaters across the entire area.

  1. Koreivienė J, Anne O, Kasperovičienė J, Burškytė V. Cyanotoxin management and human health risk mitigation in recreational waters.External Environ Monit Assess. 2014;186(7):4443-59.
  2. Backer LC, McNeel SV, Barber T, Kirkpatrick B, Williams C, Irvin M, Zhou Y, Johnson TB, Nierenberg K, Aubel M. Recreational exposure to microcystins during algal blooms in two California lakes.External Toxicon. 2010;55(5):909-21.
  3. Backer LC, Carmichael W, Kirkpatrick B, Williams C, Irvin M, Zhou Y, Johnson TB, Nierenberg K, Hill VR, Kieszak SM. Recreational exposure to low concentrations of microcystins during an algal bloom in a small lake.External Mar Drugs. 2008;6(2):389-406.
  4. Backer LC, Kirkpatrick B, Fleming LE, Cheng YS, Pierce R, Bean JA, Clark R, Johnson D, Wanner A, Tamer R. Occupational exposure to aerosolized brevetoxins during Florida red tide events: effects on a healthy worker population.External Environ Health Perspect. 2005;113(5):644-9.
  5. Kirkpatrick B, Fleming LE, Backer LC, Bean JA, Tamer R, Kirkpatrick G, Kane T, Wanner A, Dalpra D, Reich A. Environmental exposures to Florida red tides: Effects on emergency room respiratory diagnoses admissions.External Harmful algae. 2006;5(5):526-33.
  6. Nierenberg K, Hollenbeck J, Fleming LE, Stephan W, Reich A, Backer LC, Currier R, Kirkpatrick B. Frontiers in outreach and education: the Florida red tide experience.External Harmful Algae. 2011;10(4):374-80.
  7. Kirkpatrick B, Pierce R, Cheng YS, Henry MS, Blum P, Osborn S, Nierenberg K, Pederson BA, Fleming LE, Reich A. Inland transport of aerosolized Florida red tide toxins.External Harmful Algae. 2010;9(2):186-89.

Recreational Activities

People can swallow contaminated water while they are swimming or playing in the water. Active water sports (like water-skiing) pose a higher risk of accidental ingestion 1. Swimmers may swallow up to 16–200 mL of freshwater (the equivalent of 0.5 – 6.8 ounces of water) during one swim 2.

Animal Exposures to Natural/Ambient Waters

Animals can become sick when they drink contaminated water, groom themselves after swimming in contaminated water, or eat toxic algae or contaminated fish and shellfish in the water. In fact, animals are at a higher risk of ingesting contaminated water because they do not avoid water that is discolored or smells bad 3-6.

Food

Freshwater

People and animals can be exposed to HAB toxins by eating fish or shellfish from a freshwater body with a HAB. Freshwater fish can become contaminated with cyanotoxins when they eat toxin-producing cyanobacteria 7.

Marine water

People and animals can be exposed to HAB toxins by eating seafood from contaminated marine (salt) water bodies. Shellfish can become contaminated when they filter and concentrate water with a HAB, and reef fish can become contaminated through the food chain (eating other animals that have accumulated the toxin) 8,9.

Drinking Water

People and pets might be exposed to HAB toxins through a contaminated tap water supply, though this is still an uncommon occurrence. Exposure to HAB toxins can occur in a healthcare setting, although this is also rare. This type of exposure can occur if patients receive a medical treatment, such as dialysis, that uses water that has not had HAB toxins removed. In 1974, 23 dialysis patients in Washington, DC, became ill when the local water source became contaminated with cyanotoxins, which are toxins from a type of phytoplankton called cyanobacteria 10. In 1996, 52 dialysis patients died and another 64 became ill in Brazil when the water used for dialysis treatment was contaminated with cyanotoxins 10.

The occurrence of cyanotoxins in drinking water can depend on the level of cyanotoxins in untreated or raw source water and the effectiveness of water treatment methods to remove them. Some public drinking water systems use surface water from lakes that could contain a HAB. A survey of 24 source water and treatment facilities between 1996-1998 in the United States and Canada found 80% of their 677 water samples contained detectable levels of microcystin, a type of cyanotoxin 11,12. Of the 80% of water samples with detectable microcystin levels, 4% of the samples exceeded the World Health Organization (WHO) drinking water guideline limit of 1µg L -1 for microcystin in drinking water 13. However, of the 4% of samples that exceeded the WHO drinking water guidelines, only two water samples were finished or treated water samples (water ready for consumption). This means that the majority of sample water contained microcystin, but the facilities could adequately remove microcystin to levels below the WHO life-time drinking water guideline.

There are currently no federal regulations in the United States on the acceptable levels of cyanobacteria or cyanotoxins allowed in public drinking water 19. However, as of June 29, 2015, the US EPA issued new health advisoriesExternal for algal toxins in drinking water. The EPA 10-day health advisory recommends limits for two types of cyanotoxins, microcystin and cylindrospermopsin. The advisory recommendation is that algal toxin levels in drinking water do not exceed 0.3 micrograms per liter for microcystin and 0.7 micrograms per liter for cylindrospermopsin for children younger than school age (<5 years of age). For all other ages, the EPA recommends that algal toxins levels do not exceed 1.6 micrograms per liter for microcystin and 3.0 micrograms per liter for cylindrospermopsin. If algal toxins exceed these levels, the public should be notified that no one should drink or boil the water.

The Environmental Protection Agency (EPA) suggests the risk of a HAB contaminating drinking water is increasing due to nutrient pollution of source waters 15 such as agricultural runoff of fertilizer containing phosphorus and nitrogen, which are nutrients that promote algae growth.

Water treatment facilities have options to remove cyanobacteria and their toxins from water during treatment. Coagulation, sedimentation, and filtration have been shown to remove between 90 and 99.9% of algae 14. However, when algae begin to die, toxins contained in the algae can be released from the algal cells 15,16. These toxins may not necessarily be removed through coagulation, sedimentation, or filtration of the water 19. However, the toxins released by algae can be treated through other processes, such as activated carbon filtration and oxidation 16. These methods are not always a part of water utility treatment processes You can find out more about your local drinking water on EPA’s website.External

Nutritional supplements

Nutritional supplements that contain algae can also pose a risk for exposure to HAB toxins. When algae are harvested to produce supplements, a toxin-producing cyanobacteria (such as Microcystis) might accidentally be collected as well 16,17.

In 1996 in Oregon, a HAB produced large amounts of the HAB toxin microcystin in Upper Klamath Lake 16. Oregon officials issued a precautionary advisory for supplements that used algae collected from the lake. The state established an allowable limit of 1 microgram of microcystin per gram of algal supplement 16. As a result of the advisory issued by state officials and consumer concern, 87 samples of algae supplements sourced from Upper Klamath Lake were tested, and 72% had levels of microcystin that exceeded this limit 16. New technologies have since been used for collecting algae to reduce the risk of taking toxic cyanobacteria from this lake 18.

References
  1. Koreivienė J, Anne O, Kasperovičienė J, Burškytė V. Cyanotoxin management and human health risk mitigation in recreational waters.External Environ Monit Assess, 2014;186(7):4443-59.
  2. Dufour A, Evans O, Behymer T, Cantu R. Water ingestion during swimming activities in a pool: a pilot study.External J Water Health. 2006;4:425-30.
  3. Work TM, Barr B, Allison MB, Fritz L, Quilliam MA, Wright JLC. Epidemiology of domoic acid poisoning in brown pelicans (Pelecanus occidentalis) and Brandt’s cormorants (Phalacrocorax penicillatus) in California.External J Zoo Wildl Med. 1993;24(1):54-62.
  4. Beltrán AS, Palafox-Uribe M, Grajales-Montiel J, Cruz-Villacorta A, Ochoa J. Sea bird mortality at Cabo San Lucas, Mexico: evidence that toxic diatom blooms are spreading.External Toxicon. 1997;35(3):447-53.
  5. Landsberg J, Flewelling L, Naar J. Karenia brevis red tides, brevetoxins in the food web, and impacts on natural resources: Decadal advancements. Harmful Algae. 2009;8(4):598-607.
  6. Bossart GD, Baden DG, Ewing RY, Roberts B, Wright SD. Brevetoxicosis in manatees (Trichechus manatus latirostris) from the 1996 epizootic: gross, histologic, and immunohistochemical features.External Toxicol Path. 1998;26(2):276-82.
  7. Ibelings BW, Chorus I. Accumulation of cyanobacterial toxins in freshwater “seafood” and its consequences for public health: a review.External Environ Pollut. 2007;150(1):177-92.
  8. Lipp EK, Rose JB. The role of seafood in foodborne diseases in the United States of America.External Rev Sci Tech. 1997;16(2):620-40.
  9. Van Dolah FM, Doucette GJ, Gulland FM, Rowles TL, Bossart GD. 10 Impacts of algal toxins on marine mammals.External In eds. Toxicology of Marine Mammals. 2003:247.
  10. Azevedo SM, Carmichael WW, Jochimsen EM, Rinehart KL, Lau S, Shaw GR, Eaglesham GK. Human intoxication by microcystins during renal dialysis treatment in Caruaru-Brazil.External Toxicology. 2002;181:441-46.
  11. Carmichael WW, eds. Assessment of blue-green algal toxins in raw and finished drinking water. Cdc-pdf[PDF – 208 pages]External Denver, CO: AWWA Research Foundation and American Water Works Association; 2001.
  12. Carmichael WW. Health effects of toxin-producing cyanobacteria: “The CyanoHABs”. Human and ecological risk assessment: An International Journal.External 2001;7(5):1393-407.
  13. Chorus I, Bartram J. Toxic cyanobacteria in water. Cdc-pdf[PDF – 400 pages]External 1999.
  14. Svrcek C, Smith DW. Cyanobacteria toxins and the current state of knowledge on water treatment options: a review.External J Envrion Eng Sci. 2004;3(3):155-85.
  15. EPA. Creating a cyanotoxin target list for the unregulated contaminant monitoring rule.External 2011.
  16. Westrick JA, Szlag DC, Southwell BJ, Sinclair J. A review of cyanobacteria and cyanotoxins removal/inactivation in drinking water treatment.External Anal Bioanal Chem. 2010;397(5):1705-14.
  17. Gilroy DJ, Kauffman KW, Hall RA, Huang X, Chu FS. Assessing potential health risks from microcystin toxins in blue-green algae dietary supplements.External Enviorn Health Perspect. 2000;108(5):435.
  18. Heussner AH, Mazija L, Fastner J, Dietrich DR. Toxin content and cytotoxicity of algal dietary supplements.External Toxicol Appl Pharmacol. 2012;265(2):263-71.
  19. Lopez CB, Jewett, EB, Dortch Q, Walton BT, Hudnell HK. Scientific assessment of freshwater harmful algal blooms. Cdc-pdf[PDF – 78 pages]External 2008.

 

References
  1. Lopez CB, Jewett, EB, Dortch Q, Walton BT, Hudnell HK. Scientific assessment of freshwater harmful algal blooms. Cdc-pdf[PDF – 78 pages]ExternalInteragency Working Group on Harmful Algal Blooms, Hypoxia, and Human Health of the Joint Subcommittee on Ocean Science and Technology. Washington, DC. 2008.
  2. Chorus I, Bartram J, eds. Toxic Cyanobacteria in Water: A guide to their public health consequences, monitoring and management. Cdc-pdf[PDF – 400 pages]External London, United Kingdom: World Health Organization; Routledge, London; 1999.
  3. Lopez CB, Dortch Q, Jewett EB, Garrison D. Scientific assessment of marine harmful algal blooms. Cdc-pdf[PDF – 72 pages]External Interagency Working Group on Harmful Algal Blooms, Hypoxia, and Human Health of the Joint Subcommittee on Ocean Science and Technology. Washington, DC. 2008.
  4. Anderson DM. Approaches to monitoring, control and management of harmful algal blooms (HABs).External Ocean and Coastal Manag. 2009;52(7):342-347
  5. Koreivienė J, Anne O, Kasperovičienė J, Burškytė V. Cyanotoxin management and human health risk mitigation in recreational waters.External Environ Monit Assess, 2014;186(7):4443-59.
Page last reviewed: December 13, 2017