Distribution of industrial contamination in a bay system

Hi science enthusiasts!
In the throws of my postdoctoral fellowship I’ve had little time to write here, but I’ve stumbled upon a necessary occasion – new paper is out!

So as some of you might know, my work focuses on understanding rapid adaptation to extreme environments. Part of this work involves understanding how populations adapt by looking at divergent phenotypes, heritability and fitness-costs. Another large part that I consider crucial in this process is understanding the selective pressures that drive adaptation better.

During my graduate degree I focused on studying anthropogenic contaminants – polychlorinated dioxins and furans (PCDD/Fs), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs). I studied populations of Gulf killifish that adapted to this chronic contamination that has been present only 50-70 years!

At that point I went out and grabbed samples (fish populations for phenotyping, fish and sediment for chemistry for chemistry) from 2 super contaminated locations and one reference site in the bay. See below:

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Fig 1. Sampling in first study of Galveston bay Gulf killifish (paper here)

In this study the contaminated sites are part of the Houston Ship Channel. The high industrial activity in that environment has left the water incredibly polluted with all the mentioned classes of contaminants. In addition, it is the main outflow for the incredibly dense Houston metropolitan area. This means that the channel is also fully loaded with many endocrine disrupting compounds (EDCs), heavy metals and other goodies.

What we found then was that when we compare the most teratogenic (inducing developmental deformities) of compounds, we see that PCBs outdo dioxins both by total presence and by toxic equivalency (meaning they are a bigger threat to aquatic life).

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Fig 2. Chemical concentrations of PCBs and PCDD/Fs in three sampling points of GBay

Since we saw such enormous concentrations of contaminants we began to wonder about the impact of such contamination on the larger bay. How does this distribute in this dynamic environment, in which ships are moving around, tidal waves are stirring sediment and organisms are migrating. We set out to sample all across the bay and determine the PCB distribution. What we found was, mostly expected, but also highly cool.

The PCBs stemming from the Houston Ship Channel actually traverse long distances and contribute to the contamination of nearby sites. Those contaminants are found in sediment, fish and standing waters of the sites near the ship channel and decrease in a gradient like fashion:

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Fig 3. Heat map of PCB contamination in GBay. Size of circles is proportion of contribution of each environmental matrix (black – sediment; gray – fish; white – passive sampler).

Look for more details on the analyses in our paper, but overall, this could have profound impacts on the aquatic biota living in those contaminated sites. We are currently studying the level of impact that a gradient of pollution has on Gulf killifish, both in phenotypic shift of optimum traits and in whole-genome shift in allele frequencies. Stay tuned!

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