Tropical hyperaccumulators of metals and their potential for phytoextraction

Wide-ranging studies of hyperaccumulators of Ni from tropical soils of ultramafic origin were first carried out by the late Professor Robert Brooks and his co-workers in the mid-1970s. Our knowledge of tropical hyperaccumulators of Co and Cu dates from the late 1970s and 1980s, much of this having come from the work on plants of metalliferous regions of Zaïre. The contributions of Brooks and his co-workers are reviewed here, other recent published work is discussed, and new information is provided from the latest analyses of herbarium material. It is clear that many areas of serpentine and other metalliferous soils in the tropics require better investigation for the presence of metal-accumulating plant species. In some cases good botanical collections have been made, but plant and soil analysis have never been carried out, while in other areas little or no botanical or biogeochemical exploration has yet taken place. The requirements and the potential for known tropical hyperaccumulators to be used for phytoextraction (phytoremediation and/or phytomining) are discussed.