The Safe Drinking Water Act (SDWA) sets a limit for mercury-a toxin to the central nervous system-at \(0.002\) \(\mathrm{mg} / \mathrm{L}\). Water suppliers must periodically test their water to ensure that mercury levels do not exceed \(0.002 \mathrm{mg} / \mathrm{L}\). Suppose water is contaminated with mercury at twice the legal limit \((0.004 \mathrm{mg} / \mathrm{L})\). How much of this water would a person have to consume to ingest \(0.100 \mathrm{~g}\) of mercury?

The Safe Drinking Water Act (SDWA) is a fundamental law in the United States that was established to protect the quality of drinking water. Passed in 1974 and amended in 1986 and 1996, the SDWA authorizes the Environmental Protection Agency (EPA) to set national health-based standards for drinking water to protect against both naturally occurring and man-made contaminants that may be found in drinking water.

The Act requires multiple actions to protect drinking water and its sources: rivers, lakes, reservoirs, springs, and ground water wells. SDWA applies to every public water system in the United States. There are currently over 151,000 public water systems providing water to almost all Americans at some time in their lives.

The SDWA not only requires water systems to regularly monitor for contaminants, including mercury, lead, and arsenic, but also involves consumers by requiring water suppliers to provide Consumer Confidence Reports (CCR) which detail water quality information to the community.

Mercury, the central nervous system toxin in question, poses significant health risks. As a neurotoxin, mercury primarily affects the brain and nerves. Short-term exposure to high levels of mercury can cause immediate symptoms such as headaches, insomnia, or tremors. Long-term exposure may result in severe neurological issues and can compromise brain function.

The toxicity of mercury and other central nervous system toxins is taken very seriously, and exposure limits are established to protect public health. The brain and spinal cord are vital components of the nervous system that base our ability to think, feel, and move; hence, the presence of toxins such as mercury in water we drink can have dire consequences on neurological health and overall well-being.

The exercise involves a critical step of converting concentration units, which is essential in chemistry and various scientific calculations. The concentration is typically expressed in mass per volume, for example, milligrams per liter (mg/L) in the context of water contamination. Understanding this conversion is necessary when we deal with measurements of pollutant levels such as mercury in water.

Often, it's required to convert between different units to align concentrations for comparison or for calculations, like converting grams to milligrams. Since 1 gram is equal to 1000 milligrams, converting a mass of mercury from grams to milligrams is as straightforward as multiplying by 1000. This step is critical in ensuring that calculations are precise and that comparisons of contamination levels against safety standards are accurate.

To determine how much contaminated water one must consume to ingest a certain amount of toxin, the calculation involves dividing the desired mass of the toxin by its concentration in the water. This fundamental concept of dilution and concentration helps us understand the point at which a contaminant becomes harmful and how to comply with health standards like those set by the SDWA.

The formula for this calculation is:
  Volume of water (L) = Mass of mercury (mg) / Concentration of mercury (mg/L)
In our example, if a person ingests water with mercury at twice the allowable SDWA limit, we divide 100 mg (the target ingestion amount of mercury) by 0.004 mg/L (the concentration of mercury in water). This calculation is vital for environmental scientists and health professionals in risk assessment and in designing appropriate public health interventions.