WATCH: Mercury exposure in fish from protected and non-protected tropical reservoirs in Zimbabwe

At the heart of environmental conservation lies the urgent need to address freshwater contamination. This was a topic eloquently unpacked by Joseph Macaulay, a PhD student at the State University of New York.

During his lecture, Macaulay shed light on mercury contamination in Zimbabwe’s freshwater systems. Specifically focusing on its impact on fish populations and broader ecological health.

Freshwater ecosystems: a crucial yet vulnerable resource

Freshwater habitats make up only 0.8% of the Earth's surface. They provide a disproportionately high share of biodiversity.

Nearly half of the world’s 36,000 described fish species inhabit freshwater ecosystems. This highlights the remarkable richness of these environments.

However, these ecosystems face unprecedented threats, particularly from human activities.

Macaulay emphasized that freshwater species are declining at an alarming rate, faster than their terrestrial counterparts.

Pollution, driven by anthropogenic activities, is among the most significant contributors to this decline.

In Zimbabwe, the intersection of economic hardship and the reliance on artisanal and small-scale gold mining (ASGM) has intensified the problem.

The role of ASGM in mercury pollution

Zimbabwe’s gold-rich regions are also home to the country’s major drainage basins.

ASGM, which uses mercury for gold extraction, has proliferated due to minimal capital requirements and economic desperation.

This informal mining practice is a double-edged sword. It provides livelihoods to impoverished communities, whilst contributing significantly to mercury emissions.

Macaulay’s data shows that ASGM is responsible for 80% of mercury emissions in sub-Saharan Africa.

In Zimbabwe alone, over 21 tons of mercury are released annually, with severe implications for both aquatic ecosystems and human health.

Assessing the impact

Macaulay’s research focused on mercury exposure in fish from reservoirs within protected and ASGM-impacted areas.

By analyzing samples from Chivero, a protected reservoir, and Mazoe, an ASGM-affected site, his team revealed stark differences.

Fish from Mazoe showed significantly higher mercury concentrations. These far exceed thresholds set by global health organizations.

The study also identified biomagnification patterns in Mazoe, where mercury concentrations increased up the food chain, posing risks to both fish health and human consumers.

In contrast, Chivero’s fish exhibited unusually low mercury levels.

This discrepancy was attributed to the reservoir’s eutrophic conditions, which promote bloom dilution, shortening food chains and reducing mercury biomagnification.

Implications for human and fish health

The findings underscore the critical need for action.

Mercury concentrations in Mazoe’s piscivorous fish exceed safe consumption levels, particularly for vulnerable populations like pregnant women and children.

Similarly, the toxicity levels threaten fish health, impairing reproduction and behavior.

Charting the way forward

Macaulay concluded with recommendations for Zimbabwe:

1. Comprehensive monitoring: establish a long-term mercury monitoring program across major freshwater bodies
2. Dietary guidelines: develop fish consumption advisories to protect human health
3. Research expansion: conduct studies on selenium’s role in mitigating mercury’s effects and investigate consumption patterns in affected communities.

This study highlights the interconnectedness of economic activity, environmental health, and public safety.

As Zimbabwe grapples with balancing economic needs and ecological conservation, Macaulay’s work provides a crucial roadmap for safeguarding its invaluable freshwater ecosystems.

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