Question

The Safe Drinking Water Act (SDWA) sets a limit for mercury-a toxin to the central nervous system \(-\) at 0.0020 ppm by mass. Water suppliers must periodically test their water to ensure that mercury levels do not exceed this limit. Suppose water becomes contaminated with mercury at twice the legal limit (0.0040 ppm). How much of this water would a person have to consume to ingest 50.0 \(\mathrm{mg}\) of mercury?

Short answer

To ingest 50.0 mg of mercury at a concentration of 0.0040 ppm, a person would have to consume 12,500 grams or 12.5 liters of water.

Step-by-step solution

Understand the Problem

Determine the amount of water needed to ingest to reach 50.0 mg of mercury when the concentration of mercury is 0.0040 ppm (parts per million by mass).

Convert ppm to mg/g

Since ppm stands for parts per million, 0.0040 ppm mercury can be converted to mg per g of water by understanding that 1 ppm is equivalent to 1 mg of substance in 1 million mg of water (which is 1 kg of water). So, 0.0040 ppm is 0.0040 mg of mercury per g of water.

Calculate the total water required to ingest 50.0 mg of mercury

To find out how much water one must drink to ingest 50.0 mg of mercury, divide the total amount of mercury by the concentration of mercury in the water. The calculation is 50.0 mg divided by 0.0040 mg/g, which gives the total grams of water required.

Convert grams of water to liters

Water has a density of 1 g/mL, which is equivalent to 1000 g/L. Therefore, convert the mass of water in grams to volume in liters by dividing the mass by 1000.

Key concepts

Understanding the Safe Drinking Water Act (SDWA)

The Safe Drinking Water Act (SDWA) is crucial legislation passed by Congress in 1974 to ensure the quality of Americans' drinking water. Under the SDWA, the Environmental Protection Agency (EPA) sets standards for drinking water quality and oversees the states, localities, and water suppliers who implement these standards.

One critical aspect the SDWA regulates is the presence of contaminants, such as mercury, in our water supply. Mercury is particularly concerning because it is a neurotoxin that can impair cognitive and motor functions, especially in children and fetuses. The SDWA enforces a strict mercury limit to mitigate these risks, mandating that water suppliers regularly test and ensure levels remain within the safe range. Understanding the intent and scope of the SDWA is fundamental in evaluating the risks associated with contamination incidents.

What Does 'Parts Per Million (ppm)' Mean?

Parts per million (ppm) is a unit of measurement often used in environmental chemistry to express the concentration of a substance in a mixture or solution. Specifically, when referring to water contaminants like mercury, ppm quantifies how many parts (by mass) of mercury there are in a million parts of the water.

To put it into perspective, one part per million approximates to one minute in two years or a single penny in $10,000. This measurement is essential for precisely quantifying low concentrations, ensuring that water quality complies with regulations like those set by the SDWA. When water providers test their water, they use ppm to report whether contaminant levels are within safe bounds.

Neurotoxin Effects of Mercury on Health

Mercury is known for its damaging neurotoxin effects on humans. Exposure to mercury can result in a variety of health issues, most notably impairing neurological development in unborn children and infants. In adults, high levels of exposure can lead to symptoms such as tremors, insomnia, memory loss, and cognitive dysfunction.

It's the potential for these adverse health effects that motivates stringent regulations like those in the SDWA. Limiting mercury concentration in drinking water is therefore not just a regulatory concern, but a critical public health measure. The neurotoxin effects of mercury underline the importance of understanding and adhering to established safety limits in environmental contexts.

Mercury Concentration Calculations

Calculating mercury concentration in water is directly related to the aforementioned ppm unit. For instance, in the exercise, we encounter a scenario where water contains 0.0040 ppm of mercury, twice the legal limit set by the SDWA. To calculate how much water containing this level of contamination a person would need to consume to ingest 50.0 mg of mercury, we use a two-step process: we first convert ppm to milligrams per gram, then calculate the volume of water needed.

The conversion is straightforward as 1 ppm is equivalent to 1 mg of substance per kg of water. The equation used to find out the total volume of contaminated water one would have to consume is given by dividing the amount of mercury by its concentration in water. The precision of these calculations is vital to evaluate the risks of mercury ingestion and to guide actions in case of contamination incidents.

The Role of Environmental Chemistry

Environmental chemistry plays a pivotal role in understanding and solving issues related to mercury contamination in water. It involves studying chemical processes occurring in the environment and the effects of human activities on these processes. In the context of the exercise, environmental chemistry helps us comprehend how mercury behaves in water, how it can be measured, and the potential impact on ecosystem and human health.

Professionals in this field use their knowledge to develop methods for testing water contamination, create guidelines for safe levels of contaminants, and craft solutions to mitigate the impact of pollutants like mercury. Environmental chemistry is the foundation for regulations such as the SDWA and is integral in protecting our natural resources and health.