Specifically, Ian is looking at alkylated polycyclic aromatic hydrocarbons (PAHs) found in creosote. One of the important goals of the study is figuring out which PAH(s) are contributing to the toxicity seen in sites contaminated with creosote.
Creosote is a tar mixture that contains hundreds of different chemicals. It is used to treat things such as telephone poles or railroad ties that are going to be out in the environment for a very long time. The creosote prevents bacteria and fungi from degrading the wood. Unfortunately, the places that create and apply creosote often end up being contaminated sites, because the mixture ends up leaking into the environment.
There are many important aspects to characterizing a contaminated site. Two of them are exposure assessments and hazard assessments. The exposure assessment studies what chemicals might be exposed to humans and animals and the hazard assessment studies the potential toxicity of those chemicals. Ian works with the Food Safety and Environmental Stewardship Program lab, measuring what chemicals are out there in the environment using stationary samplers. First, Ian and the team deploy stationary samplers in the river adjacent to a legacy site contaminated with creosote. After a month or two, the passive sampling devices accumulate those chemicals that are likely to get inside of living organisms from the water. These chemicals are then extracted from the sampler and used to investigate the toxicity of chemical mixtures.
The main research question is: which chemicals are toxic in this complex mixture, and, how do the chemicals interact in that mixture. Ian and the team he works with study these chemicals both individually and in mixtures so that they can measure chemicals in the environment, then expose laboratory organisms to those chemicals in order to understand what the effects are. While we know that we are exposed to chemical mixtures in the real-world, we don’t know much about the toxicity of these mixtures. Therefore, Ian is exploring how individual chemicals interact in mixtures, filling key data gaps. These chemicals can interact in different ways, such as becoming more or less toxic. Specifically, Ian is using a method called effects directed analysis.
Effects directed analysis is a non-targeted hazard identification technique, which means that researchers aren’t constrained to a list of target chemicals when they investigate complex chemical mixtures. In other words, Ian is just looking to see what is in the environment. This can include chemicals like PAHs, and more. Once Ian has a chemical mixture sample, he tests that sample in a zebrafish model. If the mixture is revealed as ‘hazardous’, Ian then uses chemical separation techniques in the laboratory to separate the mixture into different groups of chemicals to see which group may be causing the toxicity.
Effects directed analysis is a powerful tool because it could identify new chemicals that have not been seen at a site before. In general, when there is a contaminated site, there is a list of common chemicals that are tested for. However, that means there could be other chemicals that are never tested for, and yet could still be hazardous. In this sense, their research can provide better insight into the different types of chemicals that may be hazardous at sites contaminated with creosote.