User:Juliaczar/Microplastics

Lead
Microplastics are very small pieces of plastic that pollute the environment. Microplastics are not a specific kind of plastic, but rather any type of plastic fragment that is less than 5 mm in length according to the U.S. National Oceanic and Atmospheric Administration (NOAA) and the European Chemicals Agency. They enter natural ecosystems from a variety of sources, including cosmetics, clothing, and industrial processes.

(section condensed to remove unnecessary information)

Two classifications of microplastics currently exist. Primary microplastics are any plastic fragments or particles that are already 5.0 mm in size or less before entering the environment. These include microfibers from clothing, microbeads, and plastic pellets (also known as nurdles). Secondary microplastics are microplastics that are created from the degradation of larger plastic products once they enter the environment through natural weathering processes. Such sources of secondary microplastics include water and soda bottles, fishing nets, and plastic bags. Both types are recognized to persist in the environment at high levels, particularly in aquatic and marine ecosystems.

(moved information from other sections to create a more comprehensive lead section)

Microplastics are common in our world today. In 2014, it was estimated that there are between 15 and 51 trillion individual pieces of microplastic in the world's oceans, which was estimated to weigh between 93,000 and 236,000 metric tons. Microplastics could contribute up to 30% of the Great Pacific Garbage Patch polluting the world's oceans and, in many developed countries, are a bigger source of marine plastic pollution than the visible larger pieces of marine litter, according to a 2017 IUCN report. The entire cycle and movement of microplastics in the environment is not yet known, but research is currently underway to investigate this issue.

Additionally, plastics degrade slowly, often over hundreds if not thousands of years. After being released into the environment, microplastics can be transported via water or air, accumulating in both freshwater and marine systems. Their slow degradation, ubiquity in the environment, and continuous loading increase the probability of microplastics being ingested and incorporated into, and accumulated in, the bodies and tissues of many organisms.

(new subheading added)

Toxicity of Microplastic Exposure in Marine Organisms
Plastic particles may highly concentrate and transport synthetic organic compounds (e.g. persistent organic pollutants, POPs), commonly present in the environment and ambient seawater, on their surface through adsorption. Microplastics can act as carriers for the transfer of POPs from the environment to organisms. Low polarity at the surface of the MPs make them more hydrophobic. This hydrophobic nature allows to adsorption of hydrophobic chemicals onto the surface of microplastics. Lipid-loving chemicals like POPs (including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (such as DDT and DDE) have the right characteristics to adsorb and concentrate on the plastics hydrophobic surface forming a micelle shape-like structure. Over 100 different marine species have been studied in regard to microplastic uptake, ranging from small zooplankton to large whales .  Feeding behaviors vary among species including different feeding mechanisms and location in the water column, which has an impact on microplastic exposure, and therefore microplastic mediated POP uptake.

A variety of compounds have the ability to adsorb to microplastics. Some of the POPs that adsorb to microplastics are endocrine disrupting compounds. Endocrine disruption by plastic additives after an organism consumes microplastics may affect the reproductive health of humans and wildlife alike. Endocrine disruption was observed in a study exposing Japanese medaka fish to a combination of estrogenic and anti-estrogenic compounds, which could be present in microplastic particles. They found that altered gene expression through changes in estrogen receptors can lead to reduced fecundity in females and abnormal germ cell growth in males. Another effect of ingestion of microplastic adsorbed POPs is hepatotoxicity. One study found that Japanese medaka fish exposed to microplastic bound polyaromatic hydrocarbons (PAHs) experienced liver toxicity including glycogen depletion, fatty vacuolation and necrosis. Behavioral changes in lugworms was observed after exposure to POP adsorbed microplastics, altering their feeding behaviors and in some cases leading to mortality.

In addition to adsorbing ambient POPs from seawater, additives added to plastics during manufacture may leach out upon ingestion, potentially causing serious harm to the organism. Several studies have been conducted in order to determine the potential bioavailability of microplastic adsorbed POPs to marine organisms. Polybrominated diphenyl ethers (PBDEs), both a plastic additive and ambient contaminant in seawater, have been found to accumulate in the stomachs of short-tailed shearwaters. In this study, one-fourth of the birds had accumulated higher-brominated congeners that are not naturally found in their prey. Lower brominated PBDE congeners were also found to accumulate in rainbow fish from microplastics, indicating that uptake may differ depending on organism metabolism and diet.

Long term impacts of exposure to microplastics and the impacts on ecological functioning are still under investigation. One study on zooplankton looked at the impacts of microplastics exposure on subsequent generations that are not exposed to plastics. They found that the microplastic exposed parents produced less offspring and the non-exposed offspring also experienced decreased growth and reproduction rates. This indicates that even if microplastics are removed from the environment, it's possible that the effects of exposure could persist in younger generations.