Glen Van Der Kraak
Prof. Glen Van Der Kraak

With tens of thousands of human-made chemicals in the world today, how can we know which ones pose the greatest threats to our health and environment?

Scientific research provides a likely answer, says Prof. Glen Van Der Kraak, Department of Integrative Biology, but that research can lead to another potential problem: How to make sense of a pile of sometimes-conflicting studies on the effects of environmental chemicals?

A “weight of evidence” approach developed by University of Guelph biologists offers a new way to assess research studies, including those used in coming up with environmental regulations, says Van Der Kraak.

He and Prof. Emeritus Keith Solomon, School of Environmental Sciences, co-authored a paper published recently in the journal Critical Reviews in Toxicology. The paper describes the use of their approach to look at atrazine, a common herbicide used on important food crops such as corn, sorghum and sugar cane. They found that the chemical poses little risk to fish, amphibians and reptiles.

Looking at more than 200 published papers on the topic, the pair and their co-authors developed a scoring system to assess the strength and relevance of the experimental methods used by the papers’ authors. That allowed them to weigh evidence for effects of atrazine at concentrations found in the environment.

They found that the chemical can affect such things as expression of genes and proteins, hormone concentrations and biochemical processes. But those effects caused no health problems in animals, including clawed frogs studied by Solomon in South Africa.

“Some reports said there were negative effects on frog development,” says Van Der Kraak, who is associate dean (research) in the College of Biological Science. “Others, including our own, said there were negligible effects or only at concentrations well above what are occurring in the environment.”

He says their weight of evidence approach might help regulators in setting environmental policy.

“We all want to know the best available information is being used when making decisions, but in doing that, we need to take into account all of the available information and do it in a systematic and transparent fashion. This is one of the first instances attempting to do that.”

Currently, regulatory agencies in Canada and the United States allow use of atrazine with warnings about limiting exposure. Other countries, including several European nations, have banned the chemical. Referring to conflicting study results, he says, “The literature is rife with controversy. People tend to select literature supporting their point of view.”

Beyond atrazine, their new approach will help scientists trying to reconcile research results involving other substances, he says. “Researchers working on toxic impacts of environmental chemicals have trouble evaluating multiple studies that often give conflicting results. Our paper provides a framework that others can use or adapt.”

Solomon adds: “We think this has taken us a long way toward having a good transparent process that can be applied.”

They plan to look further at using weight of evidence for assessing some of the thousands of human-made compounds in the environment. Those range from bisphenol A in plastics to neonicotinoid pesticides implicated in pollinator declines to glyphosate weed-killers.