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Finding Nemo was right: what you flush down the drain can impact ocean creatures

DOI: http://dx.doi.org/10.1016/j.aquatox.2016.09.015

“All drains lead to the ocean,” –Gill, Finding Nemo
Picture your typical morning routine: maybe you wake up, start some coffee, find some clean clothes (on a good day), maybe take a vitamin or some medicine, brush your teeth and rush out the door. Regardless of your own unique variations on the above, typically the thought of your morning routine doesn’t really seem related to impacts to fish or other aquatic species…right? Think again.

Products we use in everyday life, like toothpaste, cosmetics, facial cleansers, and medicines do not necessarily end their life with your use. Many commercial products contain microplastics, or small bits of plastic less than a millimeter or so in size; they can be used as exfoliants or abrasives in personal care products or in air blasting technology. These tiny bits of plastic go down the drain and often aren’t removed during wastewater treatment. Eventually, they end up in waterways and oceans where they contribute to a growing mass of secondary microplastics, or tiny plastic bits from the breakdown of larger products like plastic bottles. Once in the water, plastics can be eaten by small creatures, physically blocking their digestive pathways. Or, these tiny plastics can act as “delivery boys” of persistent organic pollutants (POPs), adsorbing POPs from the environment and then transferring the chemicals into whatever critter ends up eating the microplastic.


Microplastics come in all shapes and sizes, and may come directly from commercial products or indirectly through the breakdown of larger plastic products. Image from 5Gyres, courtesy of Oregon State University.

Gross but true: pharmaceuticals in your pee

As if plastics going down the drain weren’t concerning enough, other products we ingest also find their way to sea. You literally pee or poop out residues of any antibiotics, pain relievers, caffeine from your coffee, or any other medications/substances you may be taking. Many of these compounds don’t break down easily and can travel dissolved or associated with particles into waterways, even after running through wastewater treatment.

Plastics + an antibiotic = not so happy fish

Enter the work of Elsa Fonte from the Institute of Biomedical Sciences of Abel Salazar and her colleagues. These Portuguese researchers recognized that marine organisms are exposed to a wide range of contaminants at all times, and not just one pollutant at a time (remember my post from last month about mixture toxicity?). These researchers set out to get an initial idea of how temperature, microplastics, and an antibiotic could be acting together to impact juveniles from a species of fish, the common goby Pomatoschistus microps.


The common goby is a widely distributed species in brackish waters across the Atlantic, and acts as an important prey species in habitats where it is found. Image: Ove Glenjen, own work, CC BY-SA 3.0

Simple approach to a complicated problem

Fonte and her team used a bunch of bioassays to answer their questions about plastic and antibiotic mixture toxicity. The team collected wild juvenile gobies, acclimated them to artificial clean seawater, and then subjected the fish to a number of different conditions, termed treatments. The treatments included:

Control: as a baseline, fish just hung out in the artificial clean seawater for 96 hours

Microplastics: fish were exposed to either no plastics or a solution of 0.184 mg plastic/liter of water, for 96 hours

Antibiotic: fish were exposed to concentrations of the antibiotic cephalexin ranging from 1.3 mg/l to 10 mg/l, again for 96 hours

Combinations: The fish were exposed to combinations of microplastics and four concentrations of antibiotics, at both 20° and 25°C

A number of endpoints were measured after each of the experiments to get a feel for how each treatment impacted the fish. Predation performance was assessed by giving each fish an abundance of zooplankton prey and assessing how effectively the fish caught and ate them. Following this live measurement, the fish were sacrificed and their individual tissues were checked out for two biomarkers, enzyme (ACheE) and peroxidation (LPO) activity. Biomarkers like enzyme activity may sound fancy or complicated, but they are actually great and easily measurable indicators of an organism’s condition, since you can’t necessarily ask a fish how it is feeling. These particular biomarkers were selected because damage or disruption to either or both of these pathways can mean stress across a range of internal systems in the fish.

Killer combos, back at it again…

The results of these experiments were somewhat grim. Microplastics alone and in combination impacted predation and tissue biomarkers, exacerbating the toxicity of the antibiotic. Temperature also played a role, with higher temperatures contributing to more pronounced negative signals in the experiments.

Summary of key results from Fonte et al. 2016

Treatment Significant Effect(s)?
20C + >5 mg/l antiobiotic Reduced predation
20C + microplastics No significant effect, slight inhibition of predation and AChE
25C + microplastics Mortality + reduced predation
20C + antibiotic +microplastics Reduced predation
25C + antibiotics + microplastics Reduced predation, increased toxicity at lower concentrations, negative impact on AChE and LOP
Author created summary table highlighting key findings from the article.

Why do I care if a fish doesn’t fare well with plastic and antibiotics?

The results of this paper suggest that increased temperatures along with complex mixes of pollutants, pharmaceuticals, and microplastics can work together to harm aquatic creatures in surprising ways, with the impacts more pronounced than just one of these stressors by itself. The research stresses the need for further research into microplastics and emerging contaminants like pharmaceuticals, as different species may react differently to these stressors. But what does this mean for us? In a warming world, it means we should carefully look at simple daily actions to reduce our “drain footprint”; simple steps like picking a face wash without microplastics or avoiding medication disposal via flushing can make a difference for coastal and marine species we enjoy for food, recreation, and aesthetic value.



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