Regulatory implementation of the Clean Water Act sets quality standards as maximum concentration limits (MCL) of individual elements. Applied to all single-element constituents such values are misleading. Toxic metals (arsenic, lead, mercury) are of particular concern yet concentrations of the isolated element do not reflect the various compounds in which these metals are found in rocks, soils, surface waters, or ground waters. More importantly, such elemental concentrations do not reflect bioavailability or ecotoxicity of multi-element chemical compounds.