Background
Toxic metals in drinking water can lead to severe adverse health effects. The metals and semimetals Arsenic (As), Lead (Pb), Cadmium (Cd), Copper (Cu), Zinc (Zn), Nickel (Ni), and Chromium (Cr) are particularly deleterious to human health.
Table: The Adverse Health Effects of Metals and Semimetals
| Element | Adverse Health Effects | Source |
| Arsenic | Skin and circulatory problems; cancer in the lungs, bladder, skin, kidney, nasal passages, liver, and prostate; pregnancy complications; reduced cognitive function; premature death. | “Drinking Water Contaminants” |
| Lead | Impaired cognitive function; hypertension and other heart conditions; renal disease. | Schwartz & Hu |
| Cadmium | Damage to kidneys, skeleton system, and respiratory system; cancer. | “10 Chemicals of Public Health Concern” |
| Copper | Liver damage; abdominal pain; nausea; cramps; diarrhea; vomiting; possible links to cardiovascular disease and Alzheimer’s. | “Copper: Fact Sheet for Consumers” |
| Zinc | Nausea; dizziness; headaches; gastric distress; vomiting; loss of appetite; deficiencies in nutrient absorption. | “Zinc: Fact Sheet for Health Professionals.” |
| Nickel | Allergies, cardiovascular disease; kidney diseases; cancer. | Genchi et. al. |
| Chromium | Irritation; dermatitis; ulcers; cancer; liver abnormalities; renal effects; gastrointestinal issues. | “Chromium (CR) Toxicity…” |
To protect the public from these dangerous toxins, the EPA regulates them in drinking water (“EPA Method 200.8…”). By EPA standards, each of these metals must not be present over a certain limit in parts per billion (see Home). EPA labs dedicated to water quality control measure potential contamination using inductively coupled plasma mass spectrometry.
Mass spectrometers measure amounts of specific elements by creating ions with a 1+ charge, and sequentially measuring a set of mass to charge (m/z) ratios. Since every element has a specific set of isotopes with specific masses, EPA workers can estimate the amount of an ion present with accuracy up to a fraction of a part per billion. Unfortunately, sometimes different ions can have the same mass to charge ratio, creating interferences.
Luckily, the EPA has a way to account for interferences. Different isotopes of the same element have nearly-fixed relative natural abundances. For example, 1.25% of cadmium has a mass of 106 amu, 0.89% has a mass of 108 amu, and 12.8% has a mass of 111 amu. This means that cadmium-111 is more than ten times as common in cadmium-contaminated water as cadmium-106. Relying on relative natural abundances, the EPA has developed equations to calculate the true amount of cadmium and other metals in water. These interference equations are outlined in EPA Method 200.8 and listed on the table under the Proposal tab.
Non-EPA labs sometimes use collision reaction cell technology rather than interference equations to account for interferences. For example, the ISO method for water quality control allows use of collision reaction cell technology (“ISO 17294-2:2023 Water…”). Unlike the EPA’s method, the ISO’s method is not legally enforceable and functions only as a recommendation for governments worldwide. The EPA does NOT allow the use of collision reaction cells in water quality control.
This study compares the EPA’s interference equation method for water quality control with a method using collision reaction cells. We measure the concentrations of the toxic metals in the table above in drinking water around UT campus.