Sustainable mitigation of heavy metals from effluents: Toxicity and fate with recent technological advancements

Figures & data

Table 1. Sources, toxicity and permissible limit of heavy metals by USEPA

Heavy metals	Anthropogenic Sources	Toxic effect	Permissible limit (drinking water)
Arsenic (As)	Metal processing, mining sites, timber storage, coke ovens emission, pesticide and fertilizer industries.	Accumulates inside the cell, Carcinogen	0.05 mg/L
Chromium (Cr)	Fertilizers, fossil fuels burning, oil drilling sites, metal tanneries and plating industries.	Group 1 human carcinogen	0.05 mg/L
Cadmium (Cd)	Phosphate fertilizers, battery, and plating industries.	Nephrotoxicity and Carcinogenicity, affect gastrointestinal and pulmonary tract	0.005 mg/L
Mercury (Hg)	Battery industries, pig iron, caustic soda, gold, and cement production	Chromosome breakage, bronchitis asthma and Hunter–Russell syndrome	0.002 mg/L
Nickel (Ni)	Electroplating industries	Eczematous reaction	0.1 mg/L
Copper (Cu)	Electroplating industries	Kidney damage, anemia	1.3 mg/L
Selenium (Se)	Mining, agricultural irrigation	Bronchitis, gastrointestinal disturbances	0.05 mg/L
Lead (Pb)	Mining, batteries, use of lead products	Crosses the blood–brain barrier, carcinogenic, neurodegeneration	0.05 mg/L
Iron (Fe)	Metal refining, engine parts.	Seizures or coma.	0.3 mg/L
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Figure 1. Schematic depicting the sources effects and remediation strategies for heavy metals

Figure 2. Figure depicting metal accumulation in plants

Table 2. Microalgae used for remediation of different heavy metals

Microalgae name	Heavy metal	Initial concentration (mg/L)	Final concentration (mg/L)	Reference
Chlorella vulgaris	Cd	25–150	58.4	[^115]
Chlorella vulgaris	Fe	27.14	0.47	[^82]
Chlorella vulgaris	Zn	3.90	0.02	[^82]
Chlorella vulgaris	Cu	4.03	0.12	[^82]
Cladophora fascicularis	Cu	12.7–254.2	70.54	[^116]
Desmodesmus pleiomorphus	Cd	0.5–5	61.2	[^117]
Chlorella vulgaris	Cd	0.05	0.00	[^82]
Ecklonia maxima	Cd, Cu	–	–	[^118]
Chlorella vulgaris	As	0.08	0.00	[^82]
Chlorella minutissima	Zn, Mn, Cd, Cu	–	–	[^119]
Chondrus crispus	Cd, Zn	10–150	75.2, 45.7	[^120]

Table 3. Limitation and acceptability of different remediation approaches

Method	Drawbacks	Acceptability	Reference
Adsorption	Requirement of host material, Generation of secondary pollution.	Very low	[^110]
Coagulation and flocculation	Sludge generation, Requirement of additional treatment.	Low	[^109]
Membrane filtration	High operation pressure, Low permeate flux.	Very low	[^33]
Ion exchange	Low selectivity, Less economic, Generation of secondary pollution.	Very low	[^108]
Immobilization of metals	Does not provide permanent solution, Require marked demand to dispose the immobilized materials.	High public acceptability	[^112]
Phytoremediation	Low biomass, requirement for plant growth promoting rhizospheric bacteria; time-consuming process.	Low-medium public acceptability	[^121]
Microbial assisted phytoextraction	Dependent on soil, plant, metal, and microorganism type.	Very high public acceptability	[^112]
Microbial remediation	Dependent on microorganism employed, need optimum environmental conditions, high concentration of toxic metals cal kills microbes, require nutrient addition	High public acceptability	[^47]

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