Page 242 - Materials Chemistry, Second Edition

Technologies for Treatment of Heavy Metal–Contaminated Groundwater 223

Sources of heavy metals in the environment

Natural sources Anthropogenic sources
Weathering of minerals Mining
Erosion and volcanic Smelting
activities
Electroplating
Forest fires and biogenic
source Use of pesticides
Particles released by Sludge dumping
vegetation
Fertilizers

Industrial discharge
Atmospheric deposition

FIGURE 11.1 Sources of heavy metals in the environment.

out of the air onto land or the surface of roads. In this way, the air is an additional
route for the contamination of the environment. Metal-containing mechanical efflu-
ents constitute a noteworthy source of metallic contamination of the hydrosphere.
Another method for dispersal is the development of drainage water from catchment
zones that have been polluted by waste from mining and purifying units.
Heavy metals enter plant, animal, and human tissues through breathing, diet,
and manual handling. Motor vehicle exhausts are a noteworthy source of airborne
contaminants, including arsenic, cadmium, copper, nickel, lead, zinc, mercury, man-
ganese, and chromium. Water sources (groundwater, lakes, streams, and waterways)
can be polluted by heavy metals draining from industrial and consumer waste; acid
rain can fuel this procedure by releasing heavy metals trapped in soils. Plants are
exposed to heavy metals through the uptake of water; animals eat these plants; the
ingestion of plant- and animal-based foods is the biggest source of heavy metals in
humans. The sources, toxic effects, and maximum concentration levels of various
heavy metals are listed in Table 11.1.

11.3 HEAVY METAL TOXICITY
The essential heavy metals (Zn, Ca, Cu, Fe, Mn, Mg, and Mo) play biochemical and
physiological roles in plants and animals. However, some heavy metals are also potent
carcinogens and have a tendency to accumulate in biological systems. On account of
their inherently persistent nature, when heavy metal particles (Cu, Cd, and Pb) are
released or transported into the earth, they may undergo changes and can have an
expanded natural, general health, and financial effect (Sang et al., 2008). If the final
product contains a high concentration of heavy metals, it might be toxic to soil, plants,
and human health (Alothman et al., 2013; Mittal et al., 2016). Metal toxicity is the