Researchers at San Diego State University and the University of California, Davis, have found that metals, some of them toxic, accumulate to plastic debris in the ocean. However, the research also leaves many questions needing further research.
This is the kind of research that may well find its way into anti-plastic arguments even though the results, while concerning, do not prove anything about the environmental or marine health impacts of toxic metals attached to plastic debris in the oceans.
The study found that, over a 12-month study period, concentrations of aluminum, chromium, manganese, iron, cobalt, nickel, zinc, cadmium and lead attached to polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), low-density polyethylene (LDPE), and polypropylene (PP) increased over time. PP attracted less of the metals than the other plastics. Cadmium, nickel, zinc and lead are listed by the US Environmental Protection Agency as priority pollutants (toxic substances).
The concentrations of the metals attached to the plastics were very low: aluminum and zinc about 10,000 parts per billion each, chromium about 100 ppb, manganese and iron about 100,000 ppb each, cobalt less than 100 ppb, nickel up to about 500 ppb, cadmium about 10 ppb, and lead about 1000 ppb. All of these metals occur in nature. The researchers claim that plastic debris may accumulate greater concentrations of metals the longer it remains at sea, but little substantiation was given for this opinion nor was information about the chemical form in which the metals may attach to the plastic provided. This is not meant as a criticism of the study which acknowledges in its full text that much remains to be learned about adsorption of metals to plastics. The study also acknowledges that for some of the metal and plastic combinations the concentration of metal is similar to that found in ocean sediments though iron, manganese and zinc were two orders of magnitude greater than the concentrations found on seawater particulates. The study does not directly address the environmental or marine health issues that may or may not be associated with its findings.
This is clearly an area of research worth pursuing. Metals may well be adsorbed on to the surface of plastics. This may be a problem or may not be a problem. This may happen with plastic used packaging for beverages as well as in the oceans. Maybe there are good applications for use of plastics to remove toxic metals from water. The fact is that this research leaves us with far more questions than it provides answers.
The research paper Long-Term Sorption of Metals Is Similar among Plastic Types: Implications for Plastic Debris in Aquatic Environments is available in the online peer-reviewed journal PLOS ONE at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0085433