Top 5 Water Contaminants
Algae are vitally important to marine and fresh-water ecosystems, and most species of algae are not harmful. However, a harmful algal bloom (HAB) can occur when certain types of microscopic algae grow quickly in water, forming visible patches that may harm the health of the environment, plants, or animals. HABs can deplete the oxygen and block the sunlight that other organisms need to live, and some HAB-causing algae release toxins that are dangerous to animals and humans. HABs can occur in marine, estuarine, and fresh waters, and HABs appear to be increasing along the coastlines and in the surface waters of the United States, according to the National Oceanic and Atmospheric Administration (NOAA).
Responding to this suspected increase, the U.S. Congress in 1998 passed a law that required NOAA to lead an Inter-Agency Task Force on Harmful Algal Blooms and Hypoxia, and funded research into the origins, types, and possible human health effects of HABs. Assessing the Impact on Public Health Although scientists do not yet understand fully how HABs affect human health, authorities in the United States and abroad are monitoring HABs and developing guidelines for HAB-related public health action.
The U.S. Environmental Protection Agency (EPA) has added certain algae associated with HABs to its Drinking Water Contaminant Candidate List. This list identifies organisms and toxins that EPA believes are priorities for investigation. CDC works with public health agencies, universities, and federal partners to investigate how the following algae, which can cause HABs, may affect public health: Cyanobacteria, also known as blue-green algae, can produce toxins that may taint drinking water and recreational water. Humans who drink or swim in water that contains high concentrations of cyanobacteria or cyanobacterial toxins may experience gastroenteritis, skin irritation, allergic responses, or liver damage; Harmful marine algae, such as those associated with red tides, occur in the ocean and can produce toxins that may harm or kill fish and marine animals. Humans who eat shellfish containing toxins produced by these algae may experience neurological symptoms (such as tingling fingers or toes) and gastrointestinal symptoms. Breathing air that contains toxins from algae associated with red tide may cause susceptible individuals to have asthma attacks; Pfiesteria piscicida, a single-celled organism that lives in estuaries, has been found near large quantities of dead fish.
Scientists do not yet know whether P. piscicida affects human health. However, reports about symptoms such as headache, confusion, skin rash, and eye irritation in humans exposed to water containing high concentrations of P. piscicida have prompted public concern; Phytoplankton, or single celled marine plants, are organisms at the base of the food chain that are the food for many higher level organisms. Of the thousands of phytoplankton species, less than hundred or so are considered harmful. Those that produce toxins (poisons) or cause physical damage with sharp spines are members of groups called diatoms, dinoflagellates and raphidophytes. In the following sections we describe which phytoplankton on west coast of North America are harmful and how they cause harm to fish, marine mammals, and sometimes even humans.
The detrimental effects of a harmful algal bloom can range from cell and tissue damage to organism mortality, and can be caused by a number of mechanisms, including toxin production, predation, particle irritation, induced starvation, and localized anoxic conditions. As a result, a bloom may affect many living organisms of the coastal ecosystem, from zooplankton to fish larvae to people. The toxins produced by HAB. As noted above, only a few HAB species actually produce toxins that are poisonous to people and marine animals. The most well known HAB toxins are generically referred to as ciguatera fish poisoning (CFP), neurotoxic shellfish poisoning NSP), paralytic shellfish poisoning (PSP), diarrheic shellfish poisoning (DSP), and amnesic shellfish poisoning (ASP). Pfiesteria piscicida also produces two toxic fractions, dermonecrotic and neurologic toxins that impact fishes and humans (Bever et al. 1998, Grattan et al. 1998) (Lowitt and Kauffman 1998) (Noga et al. 1996).
Cyanobacteria also produce similar toxins that overlap with several of these general categories, including neurotoxins and hepatoxins. Symptoms of exposure to these toxins include gastrointestinal, neurological, cardiovascular, and hepatological symptoms. The algae that produce these toxins, and the specific symptoms they cause, are summarized in Appendix A. The terms "fish" and "shellfish" are associated with these illnesses because the toxins concentrate in the fish and shellfish that ingest the harmful algae; people and marine mammals may be poisoned when they consume the affected seafoods.
Other harmful algal blooms produce toxins with no identifiable effects on humans but devastating impacts on coastal living resources. For example, the flagellate Heterosigma akashiwo is thought to produce an ichthyotoxin that kills fish (Taylor and Horner 1994), resulting in significant threats to penned fish in mariculture operations.