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Metals and metalloids (an element such as arsenic or antimony with properties in between those of metals and nonmetals are common groundwater contaminants that present a risk to users of groundwater if concentrations exceed acceptable risk-based concentrations. Contamination of groundwater by metals and metalloids is most often related to industrial sources or mining and mineral processing. Their acute and chronic toxicity as well as their common occurrence, make metal and metalloid contamination environmentally significant. The behavior and toxicity of metals and metalloids can vary with the chemical composition of the groundwater and the minerals present in the aquifer. Under some conditions, a given metal or metalloid may pose little risk because it is adsorbed to the aquifer solids or precipitated from groundwater before it reaches any exposure point. In other cases these contaminants may be quite mobile, forming groundwater plumes that can pose a risk to groundwater users.

Related Articles:

• Mobility of Metals and Metalloid Contaminants in Groundwater
• Monitored Natural Attenuation (MNA) of Metals and Metalloids
• Remediation of Metals and Metalloids

CONTRIBUTOR(S): Dr. Miles Denham

Key Resource(s):

Introduction

Groundwater contaminated with metals and metalloids (collectively referred to as “metals” in this article for simplicity; Table 1) can be a major problem because of the broad spectrum of sources, the toxicity of many metals, and the difficulty in remediating metal-contaminated sites. Common metal contaminants, their primary sources, and their potential health effects, especially those that occur at U.S. Department of Defense, U.S. Department of Energy, and private sites are quite variable (e.g., Table 1). The behavior of metal contaminants in groundwater depends on the nature of the source, the chemistry of the metal, and the mineralogy of the aquifer. Regulation and remediation of metal contaminants is further complicated by the fact that metals occur naturally in aquifers, sometimes at levels that are safe for ingestion, but at other times at concentrations that naturally exceed acceptable risk-based concentrations such as Maximum Concentration Levels (MCLs).

Metal or Metalloid*	Potential Natural and Man-Made Sources to Groundwater	Potential Health and Other Effects If Concentrations are Above Risk-Based Levels	MCL(mg/L)
Antimony*	Enters environment from natural weathering, industrial production, municipal waste disposal, and manufacturing of flame retardants, ceramics, glass, batteries, fireworks, explosives, and ammunition.	Decreases longevity, alters blood levels of glucose and cholesterol in laboratory animals exposed at high levels over their lifetime.	0.006
Arsenic*	Enters environment from natural processes, industrial activities, pesticides, industrial waste, smelting of copper, lead, and zinc.	Causes acute and chronic toxicity, liver and kidney damage, decreases hemoglobin, carcinogenic.	0.010
Cadmium	May enter the environment from industrial discharge, mining waste, metal/metalloid plating, water pipes, batteries, paints and pigments, plastic stabilizers, and landfill leachate.	Replaces zinc biochemically in the body and causes high blood pressure, liver and kidney damage. Destroys testicular tissue and red blood cells. Toxic to aquatic biota.	0.005
Chromium	Used in metal/metalloid plating and as a cooling water additive. Also may enter environment from old mining operations runoff and leaching into groundwater.	Chromium (III) is a nutritionally essential element. Chromium (VI) is more toxic, causing liver and kidney damage, internal hemorrhaging, respiratory damage, dermatitis, and ulcers on the skin at high concentrations.	0.1 (total)
Copper	Enters environment from metal/metalloid plating, industrial and domestic waste, mining, and mineral leaching.	An essential nutrient in low doses. High doses can cause stomach and intestinal distress, liver and kidney damage, anemia. Essential trace element but toxic to plants and algae at moderate doses.	1.3
Lead	Enters environment from industry, mining, plumbing, leaded-gasoline, and recycling of lead-acid batteries.	Affects red blood cell chemistry; delays normal physical and mental development in babies and young children. Can cause deficits in attention span, hearing, and learning in children.	0.015
Mercury	Enters environment from industrial waste (e.g., chloralkali process), mining, pesticides, coal, electrical equipment e.g., batteries, lamps, switches), smelting, and fossil-fuel combustion.	Causes acute and chronic toxicity. Targets the kidneys and can cause nervous system disorders.	0.002
Uranium	Enters groundwater from uranium mining and ore processing operations, nuclear fuel reprocessing facilities, and potentially from exploded depleted uranium munitions.	Depresses renal function, can cause kidney damage and failure in extreme cases. More of a toxicological problem than a radiation problem, though long-term exposure can increase risk of cancer.	0.030
Zinc	Enters environment from industrial waste, metal/metalloid plating, plumbing, and is a major component of various industrial sludges.	Essential nutrient. Causes detrimental effects in humans at high doses. Can be toxic to aquatic organisms.	5(secondary)
Table 1: Several metal/metalloid contaminants of concern in groundwater. (Revised from).