A study of remote islands show debris and plastic waste alter sand temperatures, which can dramatically affect animal and environmental health.
Henderson Island, a once uninhabited paradise in the Pacific Ocean and part of the Pitcairn Island chain, is now a monument to humanity’s destructive capabilities and disposable culture.
A recent study found that along only a 2.5 km patch of the sandy beach, an estimated 18 tonnes of plastic has accumulated at a rate of several thousand pieces over many decades.(1) Until recently, the origin of this plastic has been unknown. The Island lies in the world’s third-largest marine protected area, where commercial fishing and mining are illegal. Despite this, debris is carried on shore by the South Pacific Gyre, which is a giant current that moves anti-clockwise in the direction of the East Beach. Most of the plastic is thought to have come from South America and passing ships, consisting of netting, fishing devices, razors, shoelaces, bottle caps, and even laundry baskets. Undoubtedly, this poses a significant health risk to animals through ingestion that can lead to chemical leaching induced organ failure and bioaccumulation, or even starvation due to inability to process plastics that simulate a feeling of fullness. However, it was recently found that not only did these single-use items pose a direct physical risk to the Island’s inhabitants, but they also affect the sand temperatures that are necessary for the survival of heat sensitive beach dwellers.
A team led by Jennifer Lavers, a marine ecotoxicologist from the University of Tasmania in Australia, continued this investigation into beach temperature measurements at Henderson Island and the similarly affected Cocos Island.(2) To track the plastic debris and sand temperatures, the team designed a network of ten, three square-foot plots between the two islands where plastic debris was located. Temperature sensors were placed at both 2 and 12 inches below the sand to measure variability with depth. Attempts to find a control quadrat with zero debris left the researchers empty handed, as the debris was ubiquitous along the shores. Instead, they settled on patches with the least debris.
Figure1. Low vs. High density quadrants used for temperature measurement.
Data was collected for a three-month period on both an hourly and daily basis. In the shallow sensors, temperature reached a maximum of 2.5 degrees C hotter between the low and high-volume plastic sites. The daily minimums in contrast dropped approximately 1 degree C more for high volume versus low volume sites. The temperature differences in the deeper senses showed more stability, with the effect dissipating completely with higher plastic layer thickness. This was an indication that temperature changes are not a result of thermal conductivity, but rather through infrared radiation and reduced convection. These results make sense, as plastic debris buried at 10 cm of depth accounts for 68-93% of beach debris, acting as a shield for the deeper layers from infrared transfer.
The team is currently investigating potential reasons for this circadian cycle change and have posed potential reasons for the temperature patterns. During the daytime it is suggested that the plastic acts through an insulating effect, trapping heat and moisture like a greenhouse. Alternatively, during the nighttime the cooling effect is considered more challenging to explain. Potentially the plastics in the sand allow pathways for water and air to dissipate heat more quickly without direct sun exposure at night.
Although these temperature variations seem minimal, a mere one- or two-degree difference can have significant impacts on coastal animal life. Tropical temperatures are typically very stable, so equatorial animals have adapted to live in very narrow niches. Plastic accumulation is likely to influence the abundance of crab species and diversity found throughout these beaches. For cold-blooded species like sea turtles, thermal properties are incredibly important to daily function. Sea turtles bury their eggs in the sand on these beaches, and nest temperature has been tied directly to sex ratios of baby turtles. Warmer nests can lead to higher femininization rates, and even has impacts on fitness and success, as larger hatchlings typically come from cooler nests. Similarly, shore and seabirds that rely on these beaches for nesting could be impacted, as plastics can be stored in their nesting materials that will impact the egg and chicks that develop.
Temperature changes can also affect the microscopic environment of these communities as well. Bacteria and smaller invertebrates are highly temperature insensitive, so this could lead to extinctions and thriving of different species. Plastic-driven temperature increases can also lead to greater spread of known diseases like avian malaria, with these negative changes impacting species through the entire food chain. Leaching of the chemicals in plastics is also still a generally not well studied process. These chemicals can be dangerous for animal, human, and vegetation around the world. This is in conjunction with the growing popularity of plastic breakdown into microplastics that are a significant health concern.
These changes in soil biota can have a destabilizing effect on ecosystems, so addressing this problem is an increasing concern. Some experts claim that it is too late to clean up the plastic waste that is accumulating. Instead, focus should be put onto mitigating other threats and buffering current populations from receiving significant effect by these changes.
These plastic-driven temperature changes are not isolated to these locations and will have significant implications on global environmental health. The foundation of this problem is deeply rooted in single-use plastic consumption globally. These changes act as a wake-up call to start addressing global supply chains focused on single-use products. To help solve this problem, consumers should be more conscious that plastic shouldn’t be used as a cheap commodity to be thrown out, and focus on using a more circular materials economy.
The findings of this research has been published in the Journal of Green Chemistry:
Lavers, J. L.; Rivers-Auty, J.; Bond, A. L. Plastic Debris Increases Circadian Temperature
Extremes in Beach Sediments. J. Hazard. Mater. 2021, 416, 126140. https://doi.org/10.1016/j.jhazmat.2021.126140
References
2) Lavers, J. L.; Rivers-Auty, J.; Bond, A. L. Plastic Debris Increases Circadian Temperature
Extremes in Beach Sediments. J. Hazard. Mater. 2021, 416, 126140.