Director's Blog

Tracing contaminants of public health concern through aquatic food webs

Posted by CRI Programs   |   April 7, 2017

World Health Day was created in 1948 by the World Health Organization (WHO) and is celebrated every April 7th to mark its founding. The annual day of action provides an opportunity to draw attention to health concerns for people all over the world.

Researchers at the Canadian Rivers Institute (CRI) are dedicated to understanding and advancing the science of aquatic ecosystem health. One CRI Science Director, Dr. Karen Kidd and her team of graduate and honours students and technical staff at the University of New Brunswick Saint John (UNBSJ), is making the link to human health by tracing the existence of persistent contaminants of public health concern in aquatic systems around the world.

“There are many examples where human diseases are related to environmental conditions and increasing evidence that some human diseases are on the rise because of our exposure to chemicals,” says Dr. Karen Kidd, a professor of biology and a Tier 1 Canada Research Chair in the Chemical Contamination of Food Webs.

Dr. Kidd’s research focuses on how energy flows through food webs; how this influences aquatic contaminants; and why some water bodies and their food webs are more contaminated than others. She has a special interest in mercury, examining if and how it accumulates to levels that can cause health effects in fish at the top of the food chain, in fish-eating wildlife, and ultimately, in fish-consuming humans. Fish consumption is the main route of human mercury exposure.

Dr. Karen Kidd and her team of graduate and honours students conduct field work in a diversity of aquatic ecosystems around the world.

Dr. Kidd’s research is advancing the understanding of how global processes and gradients such as latitude, temperature, species diversity, and nutrient inputs affect where contaminants end up in aquatic ecosystems. She has conducted whole-ecosystem studies in a variety of climates, ranging from the Long-Term Ecological Wetlands Area near Gagetown, New Brunswick; the Experimental Lakes Area near Kenora, Ontario; lakes in the Arctic; temperate regions in the Canadian Boreal Forest; central and southeastern Africa; to most recently, systems in Norway and Sweden.

Much of this research is showing how the fate of contaminants can be affected by a climate gradient- a proxy for climate change.

“Our project in Norway and Sweden is focused on how climate change is influencing the fate of mercury in aquatic systems. We are sampling a number of lakes across a latitudinal gradient to understand the influence of temperature on the fate of mercury in food webs. We’re hoping the southern lakes will give us a sense of what could happen in the northern lakes as the climate continues to warm,” says Dr. Kidd. “When we understand which lakes and fish species are greater accumulators of mercury, we have a better understanding of where wildlife and humans are at greater risk from exposure to this metal.”

This investigation is critical as mercury is a contaminant with a long lasting legacy. Most of the mercury in the atmosphere is from releases from past and current human activities such as gold mining, fossil fuel burning and industrial and domestic uses, and remote locations are being contaminated from its global release and distribution in air currents.  Once deposited in aquatic systems, mercury is converted by bacteria to an organic form – methylmercury – that concentrates through aquatic food webs to elevated levels in fish and that can affect the nervous system and reproduction in fish, wildlife and humans. According to Environment and Climate Change Canada[1], over 90% of fish advisories in Canada are due to mercury, which can have health effects on human neurological, immune and reproductive systems.

“There is a lot of global interest in reducing mercury exposures,” says Dr. Kidd. “Especially for Indigenous communities that rely heavily on fish as part of their traditional diets, and people in communities near industrial releases.”

There is good news for this global health issue though. The Minamata Convention on Mercury is a global treaty that was adopted in 2013 and it includes bans, phase-outs, control measures and regulations to decrease the number of products and processes, emissions and releases of mercury worldwide. One hundred and twenty eight countries have signed on to the treaty and it is currently being ratified. Other global treaties like the Stockholm Convention on Persistent Organic Pollutants have been very effective at reducing contaminants in fish, wildlife and humans.

Dr. Karen Kidd and her team analyze tissues, sediments and water for mercury, metals, pesticides, algal toxins, and emerging contaminants such as pharmaceuticals at the Environmental Chemistry Laboratory at the University of New Brunswick Saint John. Photo Credit: Rob Blanchard, UNB Media Services

“For my part, I want to know which lakes and rivers, and particularly which fish in those systems, are at greatest risk of accumulating mercury. The goal is to develop models that will predict which waterways contain fish with the highest mercury levels as this information is crucial for the protection of wildlife and human health,” says Dr. Kidd.

To undertake this world-leading research, Dr. Kidd has set up state-of-the-art facilities at UNBSJ that includes wet and dry labs and equipment to analyze tissues, sediments and water for mercury, metals, pesticides, algal toxins, and emerging contaminants such as pharmaceuticals. In addition to the analytical abilities, the laboratory has equipment that researchers and students need to identify invertebrates, sample fish and process tissues for stable isotope analyses.

Her Environmental Chemistry Laboratory is currently involved in research in a number of countries around the world and often hosts graduate students from other countries such as Chile, Mexico, Germany, France and Spain.

Dr. Kidd sees her research on contaminants in aquatic ecosystems as critical for providing warning signals for potential public health issues. “We know that fish, wildlife and humans respond in similar ways to contaminants.  If we see health issues in fish there is good motivation to also examine the health of people living in that area.”

And those further investigations, argues Dr. Kidd, should be more collaborative and interdisciplinary. “There is growing awareness that environmental scientists should be working more with researchers focused on human and animal health to share approaches and knowledge and, ultimately, identify more effective ways to improve global health. When the environment is healthy, everyone benefits.”

[1] Environment and Climate Change Canada. 2016. Canadian Mercury Science Assessment. Accessed at:

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