Toxic leaching from plastics endangers sea birds
Plastics that break down rapidly are a major source of heavy metal contamination. James Mitchell Crow reports.
Plastics designed to biodegrade are not necessarily “environmentally friendly”. Richard Banati and his colleagues at the Australian Nuclear Science and Technology Organisation (ANSTO) have shown that small fragments of degrading plastics in the ocean are a disproportionate source of heavy metals, potentially exposing animals in the marine environment to more of these toxins as a result.
Perched at the top of the marine food chain, migratory seabirds such as flesh-footed shearwaters are ideally placed to speak for this ecosystem’s health. “They are a sentinel species,” Banati says. The food they eat can be contaminated, and they often swallow coloured pieces of the plastic itself, probably after mistaking them for prey. The amount of plastic that accumulates in their stomachs can account for 10% of their body weight.
Flesh-footed shearwater numbers are in decline, and Monash University marine biologist Jennifer Lavers is investigating whether plastic pollution is playing a role. She approached the ANSTO team for help.
Some plastic contaminants can be harmful even in small amounts, so very sensitive analytical instruments were needed. “We have an exquisite infrastructure that allows us to measure atoms at very, very low concentrations,” Banati explains. The team aimed to identify what contaminants the plastics carry, and whether those contaminants could be getting into the birds.
At the Australian Synchrotron in Melbourne, they used a technique called x-ray fluorescence to identify and precisely map the distribution of trace metals in plastic pieces found in birds’ stomachs. Using the same technique, they found birds’ feathers containing some of the metals, suggesting they might be entering the birds' systems. They then used the technique of neutron activation analysis at the OPAL reactor in Sydney to measure the trace quantities of each specific metal present.
The team found that plastic may be a substantial source of metal pollutants in the marine food web. Lead, for example, is an additive in certain specialised plastics, and can be released as the plastic degrades.
Is the strategy of making things degradable a good one,
or should the emphasis be on recyclability?
But the data also show that plastics are a pollution sink. In a process known as adsorption, metals that have accumulated in the ocean over decades can build up on the surfaces of plastic pieces, potentially delivering a concentrated dose into the stomachs of any seabirds unfortunate enough to swallow them. Some of the plastic pieces from the shearwaters’ stomachs tested had significant coatings of arsenic.
In plastics that quickly break down into small pieces, the effects of leaching and adsorption are likely to be exacerbated. Not only will more contaminants be released, but the more that the plastic breaks up the greater the surface area exposed to adsorb metals.
The data raise the possibility that plastic in a bird’s stomach could be a source of toxic metals transferring into the bird. Next, the team plans to establish whether plastic contaminants cause significant biological stress to the birds. By tagging and tracking individual birds, they aim to measure how contaminant dose impacts bird health. Answering this question is only made possible by a combination of dedicated fieldwork and access to the unique sensitivity of nuclear techniques, such as neutron activation, Banati says. “You couldn’t even think of conducting research like that if you weren’t able to measure the most minute concentration.”
An unexpected consequence of the research is the broader questions it raises about what we want from plastics, Banati adds. Is the strategy of making things degradable a good one, or should the emphasis be on recyclability? “There’s a fair bit of effort and intelligence that goes into producing new plastics, and it is all very meritorious work. But have we actually put enough thought into understanding the full lifecycle of the plastic material?” he says.
It’s not just shearwaters that could benefit. In the longer term, Banati wants to expand the research to include the effect of trace environmental contaminants in people. “As fellow apex predators, one would assume that humans are being affected in a similar way.”