This paper makes a general review of phytoremediation emphasising a bit on phytoextraction, in terms of factors that affect it and possible enhancements of such factors for optimization. Phytoremediation is a diverse collection of plant-based technologies that are used to clean contaminants such as heavy metals and metalloids (HMs) from environments, especially soil and water bodies. HMs are toxic to most biota, but some plants take them up through their rhizosphere and accumulate them in their tissues without suffering the toxicity effects, thereby reducing the amounts in contaminated sites. Such plants are commonly referred to as hyperaccumulators. This exceptional ability has in recent years been explored and employed as the best technique for remediation of contaminants environments laden with hazardous contaminants. Several factors play a role in hyperaccumulation of HMs. They include but not limited to, primarily the capacity of the plant to produce biomolecules (e.g. organic acids, phytochelatins, metallothioniens, HMATPase and a number of transporters) that play a role in HMs uptake, transport, translocation, and chelation to detoxify them, sequester and store them away from physiologically active sites in cells. This can be enhanced by genetic engineering. Second is a set of factors that influence capacity of soil to avail the HMs in the form that can be taken up by plants (e.g. pH, CEC and organic content ). Capacity of soil can be helped by additives (e.g. EGTA, EDTA and EDDHA ) and some microorganisms (e.g. plant growth promoting bacteria, PGPB and arbuscular mycorrhizae fungi).

Keywords: Phytoremediation, Hyperaccumulators, Heavy metals