Cyanotoxins treatment
Article

Cyanotoxins treatment strategies for water utilities

The last couple of years, many newspaper headlines were reporting animal poisonings and deaths from drinking or swimming in contaminated with cyanobacterial blooms water sources.

Epidemiological evidence has proven the issue does not limit only to animals, as symptoms of poisoning were detected in humans following a consumption of drinking water containing cyanotoxins (cyanobacterial toxins).

Health risks associated with cyanotoxins

Quick development of symptoms and short-term severe health effects are the most common health hazards related to the presence of cyanotoxins. Groups associated with higher risk for developing intense symptoms include children who drink a greater volume of water in proportion to body weight than a grownup, or entities who are at risk of damage to organs such as dialysis patients, or individuals with liver disease.

Research also shown that exposure to microcystin toxins is associated with non-alcohol related liver disease and may possibly promote tumour growth. Thus, it is both a long-term exposure to low toxin levels as well as the short-term health effects with high toxin levels that both deteriorate health. For water utilities managers, this means it is crucial to know if drinking water contains blue-green algae and associated microcystin toxins. It is essential to comply with the current drinking water guidelines for toxins to ensure risk to public health is minimised.

Health Impacts of Cyanotoxins in humans

  • Headache
  • Shortness of breath
  • Abdominal pain
  • Kidney damage
  • Liver inflammation

What causes tastes and odours in water supplies?

Unpleasant taste and odour compounds are mainly caused by the presence of two metabolites produced by a range of cyanobacteria and actinomycete bacteria 2-methylisoborneol (MIB) and geosmin. They are important indicators of drinking water quality and acceptability and may be subject of customers complaints. They are evident at very low levels (from 500 cells mL-1 ), therefore early water treatment is advised. Taste and odour compounds are more common issue during warmer months, when higher temperatures favour algal growth. Despite objectionable taste or odour of water, it may not be unsafe to drink. Contrariwise, the absence of compounds does not guarantee that water is safe for consumption. To address it, e.g. the Australian Drinking Water Guidelines distinguish two different types of guideline value: a health-related guideline value and an aesthetic guideline value.

Drinking water guidelines

Drinking water quality guidelines advise tolerable levels for components that can be dangerous to public health and therefore are important for water supply authorities. Respective states, regions, or countries develop guideline values based on The World Health Organisation (WHO) Guidelines for Drinking Water Quality that exhibit a scientific agreement on the health hazards presented by chemicals and microbes in drinking water supply. These guidelines are fundamental in development of risk management strategies. Examples of guideline values for the concentration of total microcystins in drinking water that must be met in individual countries are as follow:

  • Australia 1.3 μg L-1
  • South America 1.0 μg L-1
  • Canada 1.5 μg L-1
  • WHO 1.0 μg L-1
  • United States of America – Cyanotoxins are currently accepted as unregulated contaminants and may require regulation under the Safe Drinking Water Act.

What should water managers monitor?

Firstly, dealing with cyanobacteria in the drinking water reservoir, it is worthwhile to know the species present, dissolved toxins, cell counts, and taste and odours compounds. The latter cannot be directly linked to toxicity of cyanobacterial blooms; therefore, it can only be used as a mean of comprehensive assessment and not as a base of a warning system for a toxic cyanobacterial bloom. The assessment facilitates understanding the extent of the cyanobacteria problem. Depending upon the results, management can implement:

  • the Alert Levels Framework,
  • drinking water guidelines,
  • control measures or,
  • water treatment

Microscopic examination and enumeration are commonly used to determine the specie and estimate cell abundance for colonial and filamentous cyanobacteria. The outcomes are frequently specified as cell mL-1 and can be later used in the Alert Levels Framework to evaluate the reservoir towards its cyanobacterial load. Ensuring safety of drinking water supply, it is useful to determine the specie of possibly toxic cyanobacteria.

Based on this information it is possible to elect analytical technique suitable for establishing toxin levels. Another method of detecting cyanotoxins are real-time monitoring programs collecting parameters such as Phycocyanin, which can allow for an early warning of toxic cyanobacterial bloom.

Nutrients and the growth of cyanobacteria

A variety of approaches has been used for the risk assessment of the growth of cyanobacteria blooms based on the correlation of environmental factors. A principal underlying hypothesis of the “susceptibility” or “vulnerability” assessments is that there is a relationship between phosphorus loading to a freshwater reservoir and algal productivity and biomass.

The main nutrients affecting the health of water bodies’ ecosystems are nitrogen (N) and phosphorus (P). Algae and aquatic plants rely on these nutrients for their growth naturally.

Human activities produce a significant surplus of nitrogen in the air either as nitrogen oxides or ammonia. It ends up deposited back onto land and washed into nearby water bodies.

It is estimated that atmospheric deposition over land has increased threefold. Extensive atmospheric N deposition leads to N-saturation of watersheds and exporting nitrate further to streams, lakes, and estuaries.

What can be done to control nutrient inputs?

The primary nutrient sources are commonly from the catchment, or internally derived from sediment. Long-term, it is beneficial to manage catchments in order to diminish the external load, however it is expensive, complex, and usually not enough by itself to eliminate cyanobacterial blooms. Studies show that control of external nutrient sources often does not decrease the nutrient loads and algal blooms in water bodies. Lakes seem to respond very slowly to nutrient control interventions. This is because the nutrients remain in deposits for long term. They replenish algal blooms and trigger further eutrophication.

A more efficient restoration method is to control algal growth, which helps prevent further accumulation of nutrients in the deposits. The main algae control methods include chemical control, aeration, mixing, and ultrasound. The ultrasonic algae control technology is considered safest and environmentally-friendly solution for eutrophication from nutrient pollution. It is harmless for fish and plants and can be used for lakes and drinking water reservoirs.