Artisanal and small-scale gold mining and biodiversity: a global literature review

Biogeochemical dynamics and sustainable remediation of mercury in West African water systems

Pollution of environmental drinking water sources by mercury (Hg) in West Africa is challenging, with the need to develop strategies to understand its biogeochemical transformation and mitigation to provide clean drinking water void of Hg. This review evaluated the biogeochemical cycle of Hg in West African ecology and the mitigation of Hg contamination of drinking water sources in the West African region. The study revealed Hg-bearing mineral deposits and artisanal and small-scale gold mining as major sources of Hg in West African environment. West African countries must develop sustainable methods for removing Hg from water. However, bioremediation (including microbial and phytoremediation) and adsorption are promising methods for purifying Hg-contaminated environmental drinking water sources in West Africa. Microorganisms such as Arbuscular mycorrhizal, E. coli, Fusobacterium sp, Trichoderma viride, Gliocladium arborescens, Bascillus sp. and Brevibacterium cysticus have demonstrated the capacity to remediate Hg from the water system. Furthermore, plant species like Paspalum conjugatum, Cyperus kyllingia, and Lindernia crustacea revealed exciting capacity as phytoremediators of Hg. Activated carbon, clay and mineral clays are abundant resources in West Africa that can function as adsorbents for removing Hg during water treatment. However, future studies should focus on optimizing the field-scale application of bioremediation and adsorption methods as mitigation strategies and their long-term benefits in West Africa. It is essential that the government in West Africa fund initiatives and programmes that support the accomplishment of the Minamata Convention agreement, which favours the attainment of the sustainable development goal (SDG-6).

Assessing sediment toxicity risks with bioavailable metal fractions: new factors and index applied to the Colombian tropical Andes hotspot

Heavy metal toxicity risk assessments in sediments often rely on pseudototal concentrations, despite the higher theoretical predictive potential of bioavailable fractions. This study introduces the Bioavailable Fraction Toxicity Factor (BTf) and the Bioavailable Fraction Toxicity Index (BTI) to evaluate metal toxicity risks using a bioavailable fraction calculated as the sum of the first two steps of the Tessier sequential extraction procedure. Investigating heavy metal pollution (Cd, Cr, Cu, Mn, Ni, Pb, Zn) in the Vetas River catchment, a critical freshwater source in the Santurbán Páramo within the Tropical Andes biodiversity hotspot, the study identified artisanal and small-scale mining as the primary driver of contamination. Water and sediment of mining areas, particularly La Baja Creek and El Volcán Village, exhibited the highest concentrations of metals, with some sediment levels being categorized as strongly contaminated by the Geoaccumulation Index and Pollution Load Index and exceeding the Probable Effect Concentration threshold. Bioavailable fraction of metals in sediments were measured. Bioavailable fractions were higher in mining-affected areas, suggesting greater potential for metal release under acidic conditions. The BTf and BTI provided a more nuanced understanding of metal toxicity risks compared to pseudototal concentrations, with higher BTI values in mining-influenced sites. These findings underscore the need for mitigation measures to address heavy metal pollution and highlight the ecological importance of the Santurbán Páramo. Further research into bioremediation potential using local flora is recommended to support sustainable management practices.

Global mercury concentrations in biota: their use as a basis for a global biomonitoring framework

An important provision of the Minamata Convention on Mercury is to monitor and evaluate the effectiveness of the adopted measures and its implementation. Here, we describe for the first time currently available biotic mercury (Hg) data on a global scale to improve the understanding of global efforts to reduce the impact of Hg pollution on people and the environment. Data from the peer-reviewed literature were compiled in the Global Biotic Mercury Synthesis (GBMS) database (>550,000 data points). These data provide a foundation for establishing a biomonitoring framework needed to track Hg concentrations in biota globally. We describe Hg exposure in the taxa identified by the Minamata Convention: fish, sea turtles, birds, and marine mammals. Based on the GBMS database, Hg concentrations are presented at relevant geographic scales for continents and oceanic basins. We identify some effective regional templates for monitoring methylmercury (MeHg) availability in the environment, but overall illustrate that there is a general lack of regional biomonitoring initiatives around the world, especially in Africa, Australia, Indo-Pacific, Middle East, and South Atlantic and Pacific Oceans. Temporal trend data for Hg in biota are generally limited. Ecologically sensitive sites (where biota have above average MeHg tissue concentrations) have been identified throughout the world. Efforts to model and quantify ecosystem sensitivity locally, regionally, and globally could help establish effective and efficient biomonitoring programs. We present a framework for a global Hg biomonitoring network that includes a three-step continental and oceanic approach to integrate existing biomonitoring efforts and prioritize filling regional data gaps linked with key Hg sources. We describe a standardized approach that builds on an evidence-based evaluation to assess the Minamata Convention's progress to reduce the impact of global Hg pollution on people and the environment.