Page 245 - Materials Chemistry, Second Edition

226 Life Cycle Assessment of Wastewater Treatment

natural substances, soil composition, and pH, have a real effect on the degree of the
impact of metals on organic and biochemical properties. Heavy metals show a lethal
impact on soil biota by influencing key microbial processes and reduce the number
and movement of soil microorganisms. Heavy metals, by implication, influence soil
enzymatic activities by changing the microbial group, which orchestrates enzymes
(Shun-hong et al., 2009). An increase of metal concentration antagonistically influ-
ences soil microbial properties, for example, respiration rate and biosynthesis, which
seem, by all accounts, to be exceptionally valuable indicators of soil contamination.

11.3.2 Heavy MeTal ToxiciTy in planTs
Heavy metal toxicity in plants varies with plant species, the particular metal, its con-
centration, its compound structure, and soil composition and pH. The same heavy
metals are thought to be fundamental to the development of all plants. A few metals,
such as Cu and Zn, substitute as coenzymes and activators for protein responses.
Heavy metal toxicity has been shown to increment the action of enzymes, for exam-
ple, glucose-6-phosphate dehydrogenases and peroxidases, in the leaves of plants
grown in contaminated soil. Some heavy metals, for example, Cd, Hg, and As, are
unequivocally toxic to metal-sensitive compounds, causing developmental delay and
death of animals. Some of these heavy metals, that is, As, Cd, Hg, Pb, and Se, are
not fundamental to plant development, since they play no known physiological role
in plants. Others, that is, Co, Cu, Fe, Mn, Mo, Ni, and Zn, are fundamental compo-
nents required for the normal development and metabolism of plants; however, these
components can easily cause harm when their concentrations are higher than ideal.
Ingestion by plant roots is one of the principal routes of heavy metals in the
course of development. The adsorption and accumulation of heavy metals in plant
tissue rely on many variables, which include temperature, moisture, natural materi-
als, pH, and supplement accessibility (Jordao et al., 2006). Heavy metal accumula-
tion by plants depends on the plant species, and the proficiency of various plants
in absorbing metals is assessed by either plant uptake or soil-to-plant exchange of
metallic elements (Khan et al., 2008). The uptake of heavy metals by plants and
the ensuing accumulation along the food chain is a potential danger to animal and
human health (Sprynskyy et al., 2007). These heavy metals aggregate in the envi-
ronmentally evolved pathway through uptake at the essential producer level and after
that, through use at the consumer levels.
Heavy metals have undesirable effects on the physiological and biochemical capac-
ity of plants. The generally self-evident impacts are the inhibition of growth rate;
chlorosis; decay; leaf rolling; changed stomatal activity; diminished water potential;
efflux of cations; changes in photosynthesis; and inhibition of photosynthesis, respi-
ration, metabolism, and the activities of a few key proteins (Ashfaque et al., 2016).
Figure 11.2 shows the toxicity of heavy metals in plants.
Heavy metal contamination of vegetables cannot be ignored, as these food-
stuffs are critical parts of the human diet. Vegetables are rich sources of vitamins,
minerals, and fiber, and furthermore, have advantageous antioxidative effects.
Notwithstanding, the ingestion of excessively contaminated vegetables may repre-
sent a hazard to human health. Heavy metal contamination of food stands out among