There is an urgent need for research in Africa and other low and middle-income regions of the world to develop appropriate standards, guidelines and regulations when it comes to heavy-metal pollution in water. This was highlighted by STIAS Iso Lomso fellow Kafilat Bawa-Allah of the Department of Zoology, University of Lagos, Nigeria.
Most water sources are vulnerable to pollution. The 2017 United States’ National Water Quality Inventory estimated that 46% of US rivers, 21% of lakes, 18% of coastal and 32% of wetlands were in poor condition due to pollutants. Water becomes polluted when harmful substances – organic and inorganic – are discharged directly or indirectly into such environments. Inorganic substances include heavy metals like mercury, cadmium, lead and zinc.
“Heavy-metal pollution in aquatic ecosystems is a global problem,” explained Bawa-Allah. “Many surface waters globally are contaminated making them unsafe for aquatic life and human use. Heavy metals are natural components of the earth’s crust but the problem arises when they are released into water due to human use. Heavy-metal pollution is unique because these elements cannot be broken down nor destroyed but can be transformed from one form to another. This makes them persistent. They are also bio-accumulated in biological systems and biomagnified along the food chain.”
These heavy metals arise from activities in the electronic, chemicals and plastics industries and from agriculture. They are usually introduced via waste water which contaminates fish and other seafood consumed by humans or reach humans directly through drinking water.
Dangerous health consequences
Their toxicity makes them dangerous to humans often with long-term health consequences. Bawa-Allah highlighted Itai-Itai Disease in Japan which started in the early 1900s as a result of cadmium introduced to rice crops via contaminated water used to irrigate rice fields, as well as Minamata Disease caused by methylmercury. This caused serious neurological symptoms affecting about 2300 people with nearly 1800 deaths.
“The clinical manifestations are usually due to chronic exposure over time. They may take years to manifest and even longer to trace back to the source. With Minamata it took 24 years to make the link with mercury in the water,” said Bawa-Allah.
She explained that the critical factor in determining the toxicity of heavy metals in water is bioavailability. This is the ability of a substance to be absorbed into body tissues and reach target receptors. Metals in water can be dissolved, colloidal or particulate – with dissolved being the most bioavailable. Environmental factors including water chemistry such as pH, the presence of ions and water hardness, affect the way heavy metals behave in aquatic environments and their potential to be bioavailable. For example, with lower pH there is higher dissociation of metals and hence increased bioavailability, water hardness can reduce metal toxicity but not necessarily bioavailability, and inorganic ions can result in increased bioavailability depending on their solubility. These factors are obviously site specific.
It’s therefore important to determine threshold levels for the interactions between the metals and environmental factors to determine at which levels bioavailability and, consequently, toxicity becomes a problem.
Information on metal-bioavailability parameters has been used in the US, Europe and the United Kingdom to develop computer models to predict bioavailability of metals in surface waters and their toxicity to aquatic organisms. These then feed into environmental regulations and water-quality standards for heavy metals.
“Several bioavailability-based models have been developed, from simple empirical models to complex mechanistic ones,” said Bawa-Allah. “Several developed countries have adopted metal bioavailability-based approaches in regulatory frameworks for setting water-quality criteria targeted at protecting aquatic life.”
She highlighted the Biotic Ligand Model (BLM) used in the US and the Abbreviated BLM used in the UK and Europe.
“These are excellent, open-access, predictive tools that account for site-specific variations,” she explained. “But both have a narrow range of input parameters – limited to the geographic areas where the data were gathered.”
These countries also have guidelines for heavy metals in water – the US Environmental Protection Agency guidelines date to around the 1980s and the European Parliament and Council of the EU published guidelines from 2000 which have been revised regularly. The current guidelines for heavy metals reflect standards modelled at different levels of bioavailability. There is also compliance monitoring in UK and European waters. Developed countries like Canada, Australia and New Zealand are now revising standards to incorporate bioavailability unique to their surface water.
“For countries in Africa and many other regions standards that exist are based on US guidelines and there is no talk of incorporating the unique bioavailability parameters. Development and application of metal bioavailability-based models in African countries is limited or non-existent. We need to develop our own BLM dependent on local parameters.”
Bawa-Allah’s research aims to highlight the advantages of bioavailability-based models and evidence of reduced metal pollution in countries that have adopted these models and policies, to identify factors hindering their application in African countries, and to emphasise the need to bridge the gap through innovative research and collaboration.
“The project will provide information vital to the development and application of metal bioavailability-based models in Africa and other regions. These will guarantee adequate protection of aquatic life and sustainable use of resources to benefit present and future generations.”
However, she also highlighted the challenges – “It will take lots of work to develop locally relevant BLMs. There are no easy data in our region. Some regions do regular monitoring but in others there are no databases. Obtaining water-chemistry data is difficult. I’m trying to gather it from published data.”
“In many African countries there are challenges including equipment, facilities, infrastructure, accessing research funding and lack of trust in collaboration. It’s hard convincing governments of the importance of such research. It should be a big enough problem to get attention, however, it’s seen as easier to adopt models and guidelines than develop our own. Environmental regulation and regulatory science is vital to ensuring sustainable development, and should be given priority in governance and policy making.”
“There’s a big gap between science and policy makers with research findings often not relayed to decision makers. Change will only come if this gap is bridged. For this to happen, interdisciplinary collaboration is needed, not science in isolation,” she concluded.
Michelle Galloway: Part-time media officer at STIAS
Photograph: Noloyiso Mtembu