Assessment of metal accumulation in plants using MetPAD, a toxicity test specific for heavy metal toxicity

Abstract

Heavy metal contamination of soils is wide spread and concerns have been raised over the potential risks to humans, animals, and agricultural crops. Toxic metals are readily accumulated in some plants and may pose a threat to humans and grazing animals. The discovery of metal-hyperaccumulating plants (i.e., metallophytes) has led to phytoremediation, a soil cleanup technology consisting of using metallophytes to remove metals from contaminated soils. Our study concerns the development of a test, hereafter called MetPLANT, for assessing metal accumulation or hyperaccumulation in plants growing on contaminated soils. MetPLANT consists of extracting metals from the plant followed by the determination of heavy metal toxicity, using MetPAD. The toxicity tests were run concurrently with chemical analysis of metals in plants and extracts. The test was used to assess metal contamination of plants growing in a raw wastewater application site located in Marrakech, Morocco, and in metal-contaminated sites (mining areas and industrially contaminated soils) located in France and Albania. It was observed that zinc (up to 17,691 mg/kg) and nickel (up to 12,625 mg/kg) were the metals most accumulated in the plants. The general trend observed was an increase in metal toxicity as the total metal content of the plants or the metal content of the plant extracts increased. This simple test can be used to rapidly assess metal accumulation in plants and could be useful in phytoremediation sites for determining the potential of plants to remediate metal-contaminated soils.