User:Schw1890/Plastic pollution

Plastic pollution in freshwater ecosystems
Research into freshwater plastic pollution has been largely ignored over marine ecosystems, comprising only 13% of published papers on the topic.

Plastics make their way into bodies of freshwater, underground aquifers, and moving freshwaters through runoff and erosion of mismanaged plastic waste (MMPW). In some areas, the direct waste disposal into rivers is a remaining factor of historical practices, and has only been somewhat limited by modern legislation. Rivers are the primary transport of plastics into marine ecosystems, sourcing potentially 80% of the plastic pollution in the oceans. Research on the top ten river catchments ranked by annual amount of MMPW showed that some rivers contribute as high as 88-95% of ocean-bound plastics, the highest being the Yangtze River into the East China Sea. Asian rivers contribute nearly 67% of plastic waste found in the ocean annually, largely influenced by the high density coastal populations all throughout the continent as well as relatively intense bouts of seasonal rainfall.

Invertebrates
A study analyzing ingestion of plastics across a variety of previously published experiments showed that out of the 206 species covered, the majority of papers documented ingestion in fish. This doesn't quite mean that fish ingest plastic more than other organisms, but instead highlights the underrepresentation of plastic effects in equally important organisms, like aquatic plants, amphibians and invertebrates. Despite this disparity, controlled experiments analyzing microplastic impact on aquatic plants like the algae Chlorella spp and common duckweed Lemna minor have yielded significant results. Between microplastics of polypropylene (PP) and polyvinyl chloride (PVC), PVC demonstrated greater toxicity to Chlorella pyrenoidosa, overall negatively impacting their photosynthetic ability. This effect on photosynthesis is likely due to the 60% reduction of algal chlorophyll a associated with high PVC concentrations found in the same study. When analyzing the effect of polyethylene microbeads (origin: cosmetic exfoliants) on the aquatic macrophyte L. minor, no effect on photosynthetic pigments & productivity was found, but root growth and root cell viability decreased. These results are concerning as plants and algae are integral to nutrient and gas cycling within an aquatic system, and have the capacity to create significant changes in water composition due to their sheer density. Crustaceans have also been analyzed for their response to plastic presence. There is proof that freshwater crustaceans, specifically European crabs and crayfish, suffer entanglement in polyamide ghost nets used in lake fishing. When exposed to plastic nanoparticles of polystyrene, Daphnia galeata (common water flea) experienced reduced survival within 48 hours as well as reproductive issues. Over a span of 5 days, the amount of pregnant Daphnia decreased by nearly 50%, and less than 20% of exposed embryos survived without any immediate repercussions. Other arthropods, like juvenile stages of insects are susceptible to similar plastic exposure as some spend part of their adolescence fully submerged in a freshwater resource. This similarity in lifestyle to other aquatic invertebrates indicates that insects may experience similar side effects of plastic exposure.

Vertebrates
Plastic exposure in amphibians has mostly been studied in adolescent life stages, when the test subjects are still dependent on an aquatic environment where it can be easier to manipulate variables experimentally. Studies on a common South American freshwater frog, Physalaemus cuvieri indicated that plastics may have the potential to induce mutagenic and cytotoxic morphological changes. Much more research needs to be done on amphibian response to plastic pollution, especially since amphibians can serve as initial indicator species of environmental decline. Freshwater mammals and birds have long been known to have negative interactions with plastic pollution, often resulting in entanglement or suffocation/choking after ingesting. While inflammation within the gastrointestinal tract in both groups has been noted, unfortunately there is little to no data on the toxicological effects of plastic pollutants in these organisms. Fish have been studied the most regarding plastic pollution in freshwater organisms, with the majority of studies indicating evidence of plastic ingestion in wild-caught samples and lab specimens. There have been some attempts to look at lethality of plastics in a common freshwater model species, Danio rerio, aka zebrafish. Increased mucus production and inflammation response in the D. rerio GI-tract was noted, but additionally, researchers noted a distinct shift in the microbial communities within the zebrafish intestinal microbiome. This finding is significant, as research within the last few decades has increasingly revealed how much power intestinal microbiomes have regarding their host's nutrient absorption and endocrine systems. Because of this, plastics may have a far more drastic effect on individual organism health than is currently known so far, thus warranting the need for further research as soon as possible. Many of these findings also have been found in a laboratory setting, so more effort needs to be channeled into measuring plastic abundance & toxicology in wild populations. References