Many plastic additives – chemicals that are mixed with plastic products during manufacturing –are known to be compounds that disrupt the endocrine (hormonal) system of the human body as well as damage corals and other marine creatures.
A new study by Tel Aviv University (TAU) and the Interuniversity Institute for Marine Sciences in Eilat (IUI) examined the effect of such additives on the reproductive process and larval development of corals and other organisms commonly found in the coral reef of Eilat. The new study, published in the prestigious journal Environmental Pollution, shows that these chemicals can have species-specific effects that may damage the population structure and biodiversity of coral reefs.
The study, entitled “Limited effects of environmentally-relevant concentrations in seawater of dibutyl phthalate, dimethyl phthalate, bisphenol A, and 4-nonylphenol on the reproductive products of coral-reef organisms,” was led by doctoral student Gal Vered of IUI and TAU, and Prof. Noa Shenkar of TAU’s School of Zoology in the Wise Faculty of Life Sciences and the Steinhardt Museum of Natural History.
How did the researchers conduct their study?
The researchers focused on four organisms – a stony coral, a soft coral, a fire coral and a solitary ascidian (sac-like marine invertebrate filter feeders). These organisms play an important role in the ecology of tropical coral reefs, and damage to their reproduction and development may affect the structure of the reef community.
They also examined four chemical additives that are widely used in plastic products and have been found in seawater in tropical areas inhabited by coral reefs.
Two of these were phthalate chemicals, which are used to soften and increase the flexibility of different kinds of plastic and can be found in a wide variety of consumer products such as food packaging, toys, medical devices and adhesives. The others were 4-nonylphenol, a stabilizer used in plastic packaging and as an additive in cleaning agents, and bisphenol A, which is found in polycarbonate plastic that is used for food and beverage packaging, baby bottles, boxes and more.
The European Chemicals Agency has classified bisphenol A as a substance that may cause damage to human fertility, based on evidence found in lab animals.
Interference with their hormonal systems may affect the chances of success of these processes, and an uneven effect on the different species may lead to a change in the community’s structure and damage to the entire system.”
Doctoral student Gal Vered of the Interuniversity Institute for Marine Sciences in Eilat and TAU
“Plastic additives are chemical additives that are incorporated into plastic products during the manufacturing process,” said Vered. “These substances reach marine environments through plastic waste and wastewater. Some of them are known to activate or suppress hormonal processes, and can therefore disrupt biological systems, but their effects on organisms in coral reefs have hardly been studied.
"The structure of the coral reef population depends on the success of the reproduction, development and settlement of corals and other reef organisms," she said. "Interference with their hormonal systems may affect the chances of success of these processes, and an uneven effect on the different species may lead to a change in the community’s structure and damage to the entire system.
“Climate change, ocean acidification and ongoing anthropogenic stressors place coral reefs at existential risk. Most of the coral reefs in the world are found in developing countries where the human population is expanding rapidly and waste management is lacking,” the study's co-author said. “Steps toward preventing plastic waste from reaching the environment include proper local waste management that reduces transportation of waste, and sustainable consumption of products regulated for additives.”
The researchers conducted a series of exposure experiments in which the effects of the plastic additives were tested at environmentally relevant concentrations in seawater and at higher laboratory concentrations. The parameters measured were fertilization and larval development, survival, settlement and metamorphoses.
The environmentally-relevant concentration of 4-nonylphenol was found to inhibit larvae settlement in the soft coral, while a high concentration of the same compound damaged the fertilization, development and settlement of all the studied organisms.
The higher laboratory concentration of one of the studied phthalate chemicals only damaged the settlement of the stony coral larvae, and not of the other organisms’ reproductive products. These findings add to the accumulating evidence that plastic pollution has a selective effect on different species.
“Our findings demonstrate plastic additives’ negative and selective effects on the development and reproduction of coral reef organisms. The environmentally-relevant concentrations used in our experiments were concentrations found in seawater; alarmingly, some had deleterious effects on organisms' reproduction,” Shenkar said.
“Nevertheless, concentration within organisms’ tissues may reach higher levels as these compounds can potentially bioaccumulate," she said. "To better understand the impact of plastic additives on this endangered ecosystem, we suggest developing better methods for measuring the actual concentrations within the tissues of the organisms to produce relevant risk assessments.”
In conclusion, the researchers "emphasize the importance of proper waste management that will reduce the presence of plastic waste from reaching the marine environment, as well as the need for methods to measure the concentration of chemicals inside the bodies of organisms so as to assess the possible risk to their reproductive and developmental processes.”