Soil contamination with heavy metals (HMs) is a serious concern for the developing world due to its non-biodegradability and significant potential to damage the ecosystem and associated services. Rapid industrialization and activities such as mining, manufacturing, and construction are generating a huge quantity of toxic waste which causes environmental hazards. There are various traditional physicochemical techniques such as electro-remediation, immobilization, stabilization, and chemical reduction to clean the contaminants from the soil. However, these methods require high energy, trained manpower, and hazardous chemicals make these techniques costly and non-environment friendly. Bioremediation, which includes microorganism-based, plant-based, microorganism-plant associated, and other innovative methods, is employed to restore the contaminated soils. This review covers some new aspects and dimensions of bioremediation of heavy metal-polluted soils. The bioremediation potential of bacteria and fungi individually and in association with plants has been reviewed and critically examined. It is reported that microbes such as Pseudomonas spp., Bacillus spp., and Aspergillus spp., have high metal tolerance, and bioremediation potential up to 98% both individually and when associated with plants such as Trifolium repens, Helianthus annuus, and Vallisneria denseserrulata. The mechanism of microbe’s detoxification of metals depends upon various aspects which include the internal structure, cell surface properties of microorganisms, and the surrounding environmental conditions have been covered. Further, factors affecting the bioremediation efficiency and their possible solution, along with challenges and future prospects, are also discussed.

The effect of increasing level of cadmium in soil was investigated on biomass production, antioxidants, Cd bioaccumulation and translocation in Ricinus communis vis-à-vis a commonly studied oil crop Brassica juncea. The plants were exposed to 25, 50, 75, 100, and 150 mg Cd/Kg soil for up to 60 days. It was found that R. communis produced higher biomass at all the contamination levels than that of B. juncea. Proline and malondialdehyde in the leaves increased with increase in Cd level in both the species, whereas soluble protein decreased. The bioaccumulation of Cd was higher in B. juncea on the basis of the per unit biomass, total metal accumulation per plant was higher in R. communis. The translocation of Cd from roots to shoot was also higher in B. juncea at all Cd concentrations. R. communis appeared more tolerant and capable to clean Cd contaminated soil for longer period in one sowing than B. juncea and the former can grow in wasteland soil also in which later cannot be cultivated.

Industrialization, natural processes, and urbanization have potentially accelerated the pace and the level of heavy metals (HMs) in soil and underground water. These HMs may be accumulated in plants and animals when they take up such contaminated water, and then make their way into human food chains. Several remediation technologies have been employed to take up HMs. Diverse conventional means such as ion exchange, electrolytic technologies, and chemical extraction have been employed in the past, but the majority of these techniques are not economical for extensive projects and they need stringent control and continuous monitoring. These technologies also have low efficiency for effective removal of HMs. In this context, algae offer an eco-friendly and sustainable alternative for remediation of HMs from polluted water. The accumulation of HMs by macro and microalgae is advantageous for phycoremediation compared to other approaches that are not economical and not environmentally friendly. So, there is an urgent necessity to refine the chances of accumulation of HMs in algae, employing the techniques of genetic engineering to create transgenic species for over-expressing metallothioneins and phytochelatins, which may form complexes with HMs and store them in vacuoles to make the maximum use of phytoaccumulation while also removing hazardous metals from the aquatic habitats. This review outlines the major sources of HMs, their adverse effects on humans, the potential of algae in phytoremediation (called phycoremediation), and their uptake mechanism of HMs.