Getting the Skinny on Heavy Metals in Ocean Plastic Waste

We all know the huge issue plastic is causing in our oceans today, but as it turns out this floating waste poses yet another danger: toxic heavy metals.

Plastic poses significant risks to both our aquatic ecosystems and the humans that rely on them. The latest scientific concern on how plastics impact heavy metal toxicity in the saltwater food chain comes in to play through two mechanisms. Trace metals contribute to the overall chemical toxicity of plastic as cadmium, zinc and lead are present in the heat stabilizers and slip agents used in plastics manufacturing, and these metals can comprise up to 3% of the polymers composition^1,2. Another, even more alarming mechanism is the ability of plastic debris to sorb and accumulate trace toxic metals from aquatic and sedimentary environments^1,3-7.

Dr. Leah Bendell runs the Ecotoxicology Research Group at Simon Fraser University in British Columbia, Canada. A professor of marine ecology and ecotoxicology, her lab is part of the Department of Biological Sciences within the Faculty of Science. Ecotoxicology is a science dedicated to understanding how we humans are impacting our aquatic and terrestrial ecosystems with the overall objective of advancing knowledge and education on the fate and effects of contaminants within the environment.

With this objective in mind, Dr. Bendell and one of her grad students, Bertrand Munier, developed a study to investigate the potential role of plastics in providing a source of the trace heavy metals zinc, copper, cadmium and lead into intertidal food webs. Cadmium in particular is a major health concern for both humans and wildlife. Given it’s been estimated that by 2050 the amount of plastic in the ocean will literally outweigh the biomass of fish^1,8, and that potentially only 9% of plastic is recycled^1,9 – this is a pretty heavy problem.

Off to the beach

The first order of business: head out to the beach and collect trash. The team visited nine different urban intertidal regions at low tide within Burrard Inlet, Vancouver, B.C., Canada and picked up every single piece of plastic debris they found across 26 km of beach. That included anything from children’s toys and bicycle parts to personal hygiene and food-related items.

Back at the lab, they classified the 144 plastic samples collected into 12 polymer types, the majority (81%) of which were common household plastics like LDPE, HDPE, PVC, polypropylene, polystyrene and nylon. To get a baseline on the inherent metals in newly manufactured plastics, they also added polymer samples purchased from the local hardware store into the mix.

Honing in on the main culprits

Dr. Bendell’s been a PerkinElmer customer for over 30 years, so when the time came to start analyzing for heavy metals in the collected samples, she turned to the PinAAcle^TM 500 Flame Atomic Absorption Spectrometer. All samples were first subjected to a weak acid extraction.

Analysis with the PinAAcle 500 system resulted in a 1 µgL^-1 LLD for all metals with precision CVs coming in at 3-5%. The recovered metal was compared across polymer types to identify which contained the larger amount of each metal, and therefore determine which polymers posed the greatest risk for introducing toxic metals into intertidal food webs.

All four metals (zinc, copper, cadmium and lead) were found in all samples, with some polymers containing higher concentrations of a specific metal than others. One beach sample actually contained metal concentrations over three orders of magnitude higher than all the other samples – a slightly scary find. But the big takeaway was that the concentration and type of metals found was completely source-dependent. When the team compared metal levels between beach samples and recently manufactured ones, they found that plastic debris is indeed a sorption site for copper and lead. PVC contained the highest levels of sorbed copper and lead, not to mention inherently high levels of zinc and lead from the manufacturing process.

As 50% of the 144 samples collected were either PVC or LDPE, this study determined that PVC is likely one of the main culprits of heavy metal contamination from plastic debris in our oceans. Small bits of plastic ingested by marine life are indeed introducing heavy metals into marine food webs – and when they get an extra dose of this toxic danger with their meal, we humans do too.

Eye-opening takeaway

“Not only were these plastics serving as a way of metal getting into these lower trophic levels, but also they were a source of the metal into the water column and they can be acutely toxic,” said Bendell. “It was a little bit of an eye-opener to the multifaceted role the plastics played¹⁰.”

The team’s hope is to add to the increasing knowledgebase of how plastic debris impacts our marine environment, in this case by providing another verified pathway for the entry of contaminants into marine ecosystems. Mission accomplished.

References

1. Betrand Munier and Leah Bendell, “Macro and Micro Plastics Sorb and Desorb Metals and Act as a Point Source of Trace Metals to Coastal Ecosystems,” PLoS One, 13(2):e0191759, doi: 10.1371/journal.pone.0191759, 2018.
2. DA Vethaak, HA Leslie, “Plastic Debris Is a Human Health Issue”, Environ. Sci. Technol., 50: 6825–6826 pmid:27331860, 2016.
3. CM Rochman, et al., “Anthropogenic debris in seafood: Plastic debris and fibers from textiles in fish and bivalves sold for human consumption,” Scientific Reports, 5, Article number: 14340 https://www.nature.com/articles/srep14340 pmid:26399762, 2015.
4. CM Rochman, “Viewpoint Plastics and Priority Pollutants: A Multiple Stressor in Aquatic Habitats,” Environ. Sci. Technol., 47: 2439–2440, http://pubs.acs.org/doi/abs/10.1021/es400748b pmid:23452158, 2013.
5. K Ashton, et al., “Association of metals with plastic production pellets in the marine environment,” Marine Pollution Bulletin, 60:2050–2055. pmid:20696443, 2010.
6. LA Holmes, et al., “Adsorption of trace metals to plastic resin pellets in the marine environment, “ Environmental Pollution, pmid:22035924, 2012.
7. C Rochman, et al., “Long-Term Sorption of Metals Is Similar among Plastic Types: Implications for Plastic Debris in Aquatic Environments,” https://doi.org/10.1371/journal.pone.0085433 pmid:24454866, 2014.
8. World Economic Forum, “The New Plastics Economy Rethinking the future of plastics,” available from http://www3.weforum.org/docs/WEF_The_New_Plastics_Economy.pdf.
9. LA Parker, “A whopping 91% of plastic isn’t recycled, “ available from https://news.nationalgeographic.com/2017/07/plastic-produced-recycling-waste-oceantrash-debris-environment/.
10. Danielle Beurteaux, “Heavy Metal: The New Toxic Danger Posed by Ocean Plastic Trash,” Oceans Deeply, April 3, 2018.