Studies show that microplastic has a negative impact on the wildlife. Thus the presence of microplastic in marine species that humans consume presents a health risk to humans. This study reviews the potential health effects of microplastic in marine species on human food security and human health. Knowledge on this subject is very limited and this study pushes the boundary of our knowledge. Additional research in this area is needed to ensure human health and food security.
Plastics are found worldwide in the marine environments, with estimates predicting more than 5 trillion plastic debris afloat at seas. Plastic enters the sea via indirectly from industrial, urban effluents, or runoff from beaches and fields. Microplastic is any piece of plastic that is less than five millimeters in size with no lower limit in place. Microplastic in the marine environment can come from broken pieces of larger plastic and be introduced to the environment already small as plastic pellets. These pellets are used to create a variety of products and can even be found in facial cleaners, bath gels, and toothpaste.
It is believed that microplastics ingestion by marine life is how it mainly enters the marine ecosystem. Once they enter the organism it is possible that they enter the cardiovascular system and deposit in certain tissues. The microplastic could cause physical damage or the organism could have a reaction to the chemicals found on the pellet. The presence of microplastic has been found in fish, crustaceans, or other animals. When a human eats these animals the microplastic present in them is transferred to the human body. However, information on the potential harmful effects on the human body are available. This area of research requires further investigation.
(1) Evidence of microplastics presence
According to a study done 11 out of the 25 most fished species contained microplastic. Microplastics have been found in varying concentrations in mussels, shrimp, bivalves, and in several shellfish species. One study found that in 9% of the US and 28% of Indonesian sold fish where microplastic was present in the gastrointestinal tract. Simple gutting of the fish does not solve the issue either. It is still present in a large variety of shellfish. Recently a study has shown that microplastic was found in the muscle of the imported fish.
Other products consumed as food by humans or used in human food preparation
Research has shown that microplastic is found in a wide variety of foods. Including but not limited to canned sardines, sprats, beer, honey, sugar, drinking water in plastic bottles, beverage cartons, and tap water in some countries. Information on this subject is still limited to certain geographic locations. More quantitative and qualitative research is required to expand upon these early results. A standard system for the measurement must be put in place in order to achieve comparable data.
(2) Implications for the environment and human food security
Uncertainty and variability in data is the main issue. A proper assessment of data is difficult as there is a severe lack of available data. It has been shown that micro/nano-plastic particles can interact with toxic chemicals found in the environment. Then these chemicals leach out into the body of the animal who ingested the plastic particle. Recent studies have also shown that micro and nano-plastic are transmitted in different food webs. This leads to the amplification of plastic accumulation the higher up you go on the food chain.
Experiments with microplastic in marine life have shown varying adverse effects. Exposure to microplastic has shown higher rates of mortality, reduced feeding rate, reduced body mass, reduced metabolic rate, reduced growth, and changes in behavior responses and reduced swimming performance, decreased fertilization and abnormalities in the larva. Similarly, neurotoxicity due to acetylcholinesterase inhibition and oxidative stress, intestinal damage, and several other adverse side effects. To properly assess risk more studies on the effects of microplastics are needed with particular focus on long-term exposure.
(3) Implications for human food safety
Marine animals may act as vehicles for the transmission of various chemicals that are attached to microplastics. There are a variety of chemicals that are used during production that are incredibly toxic to animals and humans. These pollutants, carcinogens, or neurotoxins could be transferred to humans through consumption of tainted marine wildlife. Microplastics could disrupt cellular functioning, and could accumulate and magnify in certain food webs. This magnification and accumulation poses a higher toxicity risk to animals at the top of the food chain. Microplastics have also been shown to absorb heavy metals such as mercury. This is highly toxic to humans and animals and poses an enormous health risk. Recently studies have shown that these plastics have specific chemicals, microbes, and other organisms present. This “plastisphere” is of enormous concern regarding the transmission of certain pathogens and invasive species. This could potentially destroy biodiversity. However the research regarding pathogen transmission is still speculative. Research regarding the subject of transmission is very scarce. Additional studies are needed to expand upon this subject. Especially studies highlighting the contribution that microplastics play to the addition of toxic chemicals to the human diet. Global climate change may also change the interactions between plastic and the chemicals ability to latch on. Additional research is required in this area as well.
(4) Implications for human health
There is evidence showing the presence of microplastic in our food, but there is little evidence on the effects after ingestion. The adverse effects on human health have yet to be explored. Scientists speculate microplastics larger than 150 µm are unlikely to be absorbed. Microplastics smaller than 150 µm may be absorbed by the lymph system and circulatory systems leading to systematic exposure. Only microplastics smaller than 20 µm would be able to penetrate the organs, while it would have to be smaller than 10 µm to access all cell membranes including the blood brain barrier and the placenta. Recently a study tested the effects of 10 µm microplastic on the brain, and epithelial cells. They observed toxic effects at the cellular level. There is little data in this area and more is advised to have a comprehensive understanding of the absorption of these varying plastic sizes. A proper assessment of risk is improbable as there is not enough data currently. Little is known about the effect of size, shape, type of plastic, surface area, additionl pollutants, and other factors effects on absorption and human health. Microplastic found in the air must also be further studied. Therefore health effects in humans should be regarded with caution as the field is still in its infancy.
The pollution of the ocean by microplastics has negative effects on wildlife while also potentially contaminating our food supply. In order to understand the risk to human health more data is required. The effect of microplastic on human health and the routes of absorption need to be thoroughly understood. This should be explored in the future.