Dangerous concentrations of algae such as "red tides" have been consistently emerging in locations around the world. A region in Southern Australia is experiencing a nine-month toxic algae bloom that spans thousands of miles and has caused thousands of deaths across marine species. Such harmful algal blooms (HABs) produce toxins that can force municipalities to close beaches and lakes due to public health risks.
Excess amounts of nutrient input from land sources into aquatic environments, such as agricultural runoff and waste discharge, typically have been blamed as the source of harmful algae blooms. But data from a new study by University of California San Diego researchers reveals that petroleum-based plastic pollution may be amplifying these problems by removing the animals that keep algae in check.
Plastic pollution has been found in every area of the planet, from the recesses of the deep sea to Arctic sea ice. Broken down bits of microplastics have emerged as a serious health issue since they have been found in human blood and in vital organs such as the brain and lungs. In recent years, plastic developed from biodegradable materials have emerged as a safer alternative for human health and the environment.
Researchers in UC San Diego's Department of Ecology, Behavior and Evolution (School of Biological Sciences) and Department of Chemistry and Biochemistry (School of Physical Sciences) conducted a three-month study comparing the environmental effects of conventional fossil fuel-based polyurethane plastic and recently developed biodegradable plastic. The biodegradable plastic included sustainable material developed in UC San Diego laboratories and sold by the university spinoff company Algenesis.
"We see all this plastic out there but how is it changing populations of algae, bacteria, seabirds or fish? We really don't know," said Biological Sciences Professor Jonathan Shurin, the senior author of the study , which appears in the new journal Communications Sustainability. "We know algae blooms are partly due to nutrient pollution, but this study is showing that some of the algae blooms that we see around the world may also be due in part to the effects of plastic on the animals that normally control algae."
Researchers have documented how contaminated rivers flowing into the ocean can lead to a surge of excess nutrients. In such "bottom up" scenarios, excess chemicals can rapidly boost algae, which consume oxygen when they die and lead to aquatic "dead zones."
In the new study, which compared different types of plastics across 30 experimental pond ecosystems, researchers found that fossil fuel plastics can lead to "top down" effects by killing off the animals that eat algae. The experiments showed that microplastics change communities of microbes, including organisms such as algae and bacteria.
Inside the tanks with fossil fuel plastic, researchers saw the numbers of zooplankton — tiny aquatic animals that consume algae and other species, and are a food source for fish and other animals — immediately plummet. Lacking zooplankton grazers, algae concentrations quickly spiked in these tanks. In contrast, tanks tested with biologically based plastics featured a much smaller impact on zooplankton and other members of the community ecosystem.
"The petroleum plastic seemed to have a strong negative effect on the zooplankton populations," said Scott Morton, the first author of the study and a Biological Sciences graduate student. "They seemed to either die off or reduce their reproduction very quickly. Bioplastic didn't have the same effect. That cascades down to the algae. In the petroleum tanks, fewer zooplankton consuming all that algae means you have more in the system and that leads to the algal blooms that we saw."
The researchers also documented the emergence of distinct communities of bacteria growing in the presence of the plastic, but the cause is not yet clear.
"Our results indicate that microplastics may tip the balance of conditions in favor of algal blooms," the authors conclude in their study. "These results collectively illustrate that microplastics, particularly petroleum-derived plastics, may destabilize microbial community structure and function."
Although the ecological impacts of microplastics are only beginning to be studied, the authors note that transitioning to a biodegradable plastics economy would likely mitigate the environmental impact of plastics in aquatic ecosystems.
For the past decade, coauthor Professor Michael Burkart and his group in the Department of Chemistry and Biochemistry have been developing and commercializing bio-based plastics expressly designed to biodegrade in the natural environment, which can be incorporated into consumer products like surfboards, flip-flops and cell phone cases. "It is critical for us to understand how these new materials compare to traditional petroleum plastics when discarded in the environment," said Burkart. "While all man-made objects have an impact on the planet, our goal is to minimize the ecological and health hazards of these now ubiquitous materials."
The researchers are now further exploring their results by testing different types of biodegradable plastics, including " living plastic " filled with bacterial spores that break down the plastic material at the end of its life cycle.
The authors of the study were: Scott G. Morton, Gabriel Vucelic-Frick, Jonathan R. Dickey, Bhausaheb S. Rajput, Cody J. Spiegel, Dahlia A. Loomis, Sara L. Jackrel, Michael D. Burkart, Jonathan B. Shurin.
The research was supported by UC San Diego's Pathways in Biological Sciences Training Program through a grant from the National Institute of General Medical Sciences (T32 GM133351) and the Department of Energy (DE-EE0009295).
Competing interest disclosure: Burkart is the founder and holds an equity position in Algenesis Materials, which seeks to commercialize renewable materials.
