Toxicity Limits for Water Pollutants in Treated Water

Water streams may be contaminated by elements such as arsenic and lead. Photo by Si Adam

Question: “What are the arsenic, lead, etc., limits for water and wastewater treatment products?”

Wastewater treatment produces purified drinking water and less-stringently processed water used for a number of purposes. Whether or not the treatment products are used for drinking, the amount of toxins allowed in the final product is regulated by the Environmental Protection Agency. In order to answer this question from a Decoded Science reader, we describe here the sources of these pollutants and the current U.S. legislation regarding drinking water and the discharge of wastewater.

Arsenic: Sources and Effect on the Health

Arsenic (As) is an element used for several human activities. It is a very poisonous element; prolonged exposure to it or ingestion of small amounts can cause long term effects, such as cancer.

In nature, As is present in the form of various minerals, such as arsenpyirite (FeAsS) and lollyngite (FeAs₂). Leaks of these minerals into ground waters can cause contamination.

Arsenic is used in several industries and/or agricultural processes; for many years it has been used, for instance, as a wood preservative. More recent applications are in the field of electronics, as arsenic-based compounds such as gallium arsenide (GaAs) are used as semiconductors. The wastewaters from these uses may contain high concentrations of arsenic.

Lead: Occurrence and Hazards

Similarly to arsenic, lead (Pb) is also a hazardous element employed in many processes. Exposure or ingestion of lead can cause serious harm to the nervous system; young children seem particularly affected, as they may experience long-term effects, such as learning disabilities.

In nature, Pb is found in ores, such as galena (PbS), anglesite (PbSO4) and cerussite (PbCO₃). Today, its main industrial application is in the production of batteries, especially for cars. Lead is also used in construction, due to its resistance to corrosion; some lead-based compounds are employed in the manufacturing of paints, and in many electronic devices.

In the past, lead was used in many other fields, such as for plumbing in houses and as additive for fuels. In recent years, it has been replaced by other elements and/or chemical compounds, due to its adverse effect on health. These previous uses, however, can still be a cause of exposure in present days; old houses, for instance, may still have lead plumbing and, consequently, higher Pb levels in drinking water.

Click to Read Page Two: Drinking Water Safety Legislation

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