Arsenic Species Distribution and Toxicity in the Environment, Bioaccumulation, Biomethylation and Bioremediation by Microalgae: A Review

Abstract

Arsenic (As) is a noxious metalloid that has been designated a priority pollutant and is present in the environment as a consequence of both anthropogenic and natural processes. Its toxicity in environmental and biological systems depends strongly on the chemical species. Interest in arsenic and microalgae interactions is important because microalgae are at the base of the aquatic food chain, are used in animal nutrition and has potential for As phytoremediation. This paper reviewed the current information on As species distribution in the environment especially as it relates to its toxicity to microalgae as well as its bioaccumulation, biomethylation and bioremediation by microalgae using appropriate methods. Information obtained revealed that Microalgae have evolved mechanisms for dealing with As in the environment with arsBHC operon mediating the reduction and extrusion of arsenite from the cells. They accumulate large amounts of arsenic from their surroundings which could lead to toxicity, As excretion from cells, reduction, methylation or complexation with metal binding peptides like glutathione and phytochelatins. This has made them suitable as ecological indicators to give an indication of As bioavailability and also in possible applications for the process of As remediation. Microalgae are been proposed for bioremediation purposes in aquatic environment since they show a high capacity for biosorption and bioconcentration of As and most importantly since they are able to methylate inorganic As to non-toxic organic and volatile As.