Aluminum cans littering the ocean floor; source: http://oceancrusaders.org/aluminium-cans/

 

By Swati Hegde, Ph.D.

January 14, 2019

Though not discussed often, aluminum is one of the significant sources of water pollution primarily due to its abundant natural occurrence and industrial use. Aluminum is a versatile material due to its excellent properties such as lightweight, corrosion resistance, long life, and electrical conductivity. Hence aluminum finds its presence in a wide range of applications including transportation, packaging, construction, electronic hardware, and electrical transmission lines, to name a few. Naturally, the consumption of aluminum is very high reaching as high as 5.4 million metric tons in the United States in 2017 alone1.  The release of aluminum to the aquatic environment occurs through both natural and anthropogenic forms resulting from weathering of rocks, acidic springs, and volcanic activities. The anthropogenic aluminum release is a result of human activities such as industrial processes resulting in wastewater and solid waste, fossil fuel combustion, manufacturing, aluminum production, and agriculture. Alum (potassium aluminum sulfate), a chemical used in clarification of drinking water and wastewater can also be a source of aluminum if released untreated2. High levels of aluminum are observed predominantly in freshwater compared to marine water as low pH of freshwater compared to ocean water favors its solubility. Acid rain due to industrial activities is a major reason for increased aluminum levels in water as acid rain reduces water pH favoring dissolution of anthropogenic and natural forms. Hence aluminum is an inevitable source of contamination in freshwater in both urban and rural areas resulting in toxic effects on aquatic life and eventually can enter the human food chain.

Effect of Aluminum on aquatic life:

There has been a proven negative impact of aluminum on a number of beneficial freshwater algae species3. Freshwater algae are crucial to maintaining a healthy synergistic ecosystem as they increase the bioavailability of dissolved oxygen for the organisms underneath. The toxicity of aluminum on aquatic life, however, depends on various physicochemical factors such as water pH, temperature and salt level. On the flip side, use of aluminum is well known in controlling toxic algal blooms where it acts by cutting off an essential nutrient (phosphorus) supply. Even though the low concentration of aluminum in water is not extremely toxic, the downstream industrial point sources of aluminum-rich process water are a threat to the natural ecosystem. In the aquatic environment, aluminum acts as a toxic agent on animals that use gill-breathing such as fish and invertebrates, by causing a loss of their osmoregulatory function (i.e., maintaining appropriate body pressure in water by aquatic organisms by controlling the uptake of salts and ions from water)4. Aluminum can also react with other chemical contaminants in the water leading to unforeseen impacts on biodiversity. Even though it is often stated that low concentrations do not negatively impact aquatic life, chronic exposure to these levels has been observed to be toxic to certain species of aquatic plants, zebrafish, fathead minnow, rotifers, and snails5. While there is a handful of literature studying the effect of aluminum on aquatic life, this is an ongoing topic of discussion as the aluminum level in water is a function of physical, chemical and environmental conditions of an aquatic ecosystem. Nevertheless not following regulatory guidelines on acceptable aluminum levels is always a threat as this heavy metal can eventually enter the human food chain via drinking water. The flowchart presented in the recently released EPA document shows the sources, fate and effect of aluminum on aquatic life.

Conceptual model showing aluminum sources, fate of transport, and its effect on aquatic life; figure reused from EPA document Dec 20186

EPA recommendations on Aluminum levels in water

EPA’s office of water recently released a report on the toxic effects of aluminum on aquatic life. The states and tribes can obtain information via this document to establish water quality standards about aluminum under the clean water act (CWA). Even though this document provides recommendations on the basis of scientific information, one must note that it is not a regulatory guideline. Therefore, the states and tribes are not legally bound to follow this act. The Clean Water Act (CWA) Section 304(a)(l) directs the Administrator of the Environmental Protection Agency (EPA) to publish water quality criteria that accurately reflect the latest scientific knowledge. This section focuses on the type and extent of all identifiable effects on health and welfare that might arise as a result of the presence of pollutants in any body of water, including groundwater7. As required by CWA, the EPA periodically revises these criteria to ensure that the revisions accurately reflect the up to date scientific knowledge and technological progress. The last update to the quality criteria for aluminum was developed in 19888. The 2018 update of the document contains scientific data on the effect of aluminum on 13 different species of invertebrates and dataset can be found here. Table 1 provides a comparison of 1988 and 2018 national recommended aquatic criteria for aluminum.

Table 1: Comparison of the EPA’s 1988 and 2018 National recommended aquatic criteria for aluminum; table reused from the EPA document December 20186; DOC: Dissolved Oxygen Concentration

The 2018 aluminum criteria provide an acceptable range that is obtained using multiple linear regression models to normalize the toxicity data unlike the fixed values in 1988. For freshwater criteria, users can also enter specific water quality information in the Aluminum Criteria Calculator to evaluate site-specific impacts of aluminum on aquatic life. The resulting acute criterion indicates that freshwater organism would be protected if the ‘one-hour average’ concentration has not exceeded the recommendation more than once every three years on average. The chronic criterion indicates that freshwater organisms would be protected if the ‘four-day average’ concentration has not exceeded more than once every three years on average. More information on EPA recommended aluminum criteria can be found here.

 

 

 

  1. https://fas.org/sgp/crs/misc/IF10998.pdf
  2. Gidde, M.R., A.R. Bhalerao and H. Tariq. 2012. Occurrence of aluminium concentration in surface water samples from different areas of Pune city. Intern. J. Emerg. Tech. Advan. Eng. 2(7): 215-219
  3. https://www.tandfonline.com/doi/pdf/10.1080/10643389991259245
  4. https://www.ncbi.nlm.nih.gov/pubmed/24202562
  5. https://setac.onlinelibrary.wiley.com/doi/full/10.1002/etc.3901
  6. https://www.epa.gov/sites/production/files/2018-12/documents/aluminum-final-national-recommended-awqc.pdf
  7. https://www.epa.gov/sites/production/files/2018-12/documents/aluminum-final-national-recommended-awqc.pdf
  8. https://www.epa.gov/wqc/national-recommended-water-quality-criteria-aquatic-life-criteria-table