Trace Metals in Groundwater: Sources and Mobilization

Generally, the solubility of trace elements is very low, and hence they are present in very low concentrations in natural water. Their presence in aquifer water is usually not anticipated, as many have toxic effects even at low levels. This is problematic, particularly in urban and rural areas where groundwater is a chief source of drinking water. Arsenic and lead enrichment in groundwater is a generally known global toxic issue affecting millions of people in numerous countries. Chromium, cadmium, and mercury in groundwater have also caused opposing effects on public health and ecosystems. The WHO list of ten chemical substances of major public concern comprises four trace elements (cadmium, mercury, arsenic, and lead) owing to their high toxicity nature, perseverance in the environment, and bioaccumulation characteristics. Therefore, public health and environmental concerns over trace metal contamination of the environment have increased in recent years. Trace metals are present in the Earth's crust, but groundwater contamination can come from natural and/or anthropogenic sources. Aquifer type, intensity of weathering of minerals from the aquifer, precipitation frequency, infiltration water quality, and residence time are natural factors controlling the presence of trace metals in groundwater. Anthropogenic sources include waste from various industrial activities (e.g. tanning, electroplating, chemical and textile manufacturing, mining, smelting, etc.), soil contaminants, underground storage tanks, landfills, tailings ponds, municipal sewage, contaminated surface water, fertilizers, and pesticides.