Marigold (Tagetes erecta): The Potential Value in the Phytoremediation of Chromium

Environmental pollution with chromium (Cr) is harmful to humans, animals and plants, while in plants it causes diminished growth, anatomical alterations and death. In the present study, the potential value of marigold (Tagetes erecta) in the phytoremediation of Cr has been investigated. The randomized experimental design involved the exposure of plants to nutrient solutions containing 0.00, 0.04, 0.08, 0.12, 0.16 or 0.24 mmol L−1 Cr(III). Chromium toxicity was observed at Cr(III) concentrations ≥ 0.12 mmol L−1 as demonstrated by diminished growth of the aerial parts and reduced density of the root system. Increasing Cr(III) concentrations in the nutrient solution resulted in a higher bioaccumulation of total Cr in the tissues, although translocation from roots to aerial parts was not efficient (maximum value of 25% at 0.12 mmol L−1 Cr(III)). The Cr bioaccumulation was up to 11-fold greater in roots than in the aerial parts. Tagetes erecta exhibited leaf plasticity when exposed to Cr, indicating the existence of a tolerance mechanism to Cr in this species. Chromium caused a reduction in xilem vases, resulting in a plastic effect in T. erecta leaves that increased the metal tolerance in culture solution. Tagetes spp. are potential Cr hyperaccumulators; at Cr(III) concentrations up to 0.12 mmol L−1, the plants accumulated levels above that proposed for hyperaccumulators and still maintained a considerable growth and even flourished. However, this study was conducted in nutrient solution, and studies on species confirmation as Cr hyperaccumulator should be conducted in soils for further clarification.