Microplastics: from ocean to table

Estimates from 2015 suggest that since the 1950s, 7.8 billion tons of plastic had been produced – of this, around 60% has been discarded and is accumulating in the environment today as waste. Land-based plastic pollution is a major source of marine plastic pollution: an estimated 80% of marine debris is thought to originate from land-based sources.

Plastic in the marine environment turns into marine plastic litter of different shapes and sizes, broken down by UV-light from sun, salt, and other abiotic factors. Very small pieces of marine plastic litter are considered as microplastics in the environment which upon ingestion, and in some cases even exposure, affects the health of humans and marine organisms.

In this photo story, we explore the pathways and health effects of microplastics on humans. We focus in particular on Thailand, one of the world’s biggest contributors of marine plastic pollution.

Plastic pollution in Asia

Though microplastics are widely dispersed in the world’s oceans, there are several hotspots in Asia with a high abundance of microplastics. The Asia region alone contributes to more than 80% of plastic pollution, with Thailand ranking as the sixth largest global contributor to marine plastic. Factors such as high plastic consumption, high human population density and poor waste management add to Asia’s marine plastic problem.

In Thailand, high plastic consumption coupled with poor waste management and low levels of recycling on land are the main contributors to marine plastic pollution. According to Thailand’s Pollution Control Department only about 86% of the 4.2 million tons of municipal solid waste generated in Bangkok in 2016 was collected. Most of the collected solid waste is dumped in landfills or incinerated, and poor waste management in landfills causes waste leakage into waterways, eventually leading into the ocean.

Additionally, there is a low rate of with only 8% of the total Bangkok population separating their waste, which is one reason for Bangkok’s low rates of recycling – only about 4% of recyclable waste is recycled.

Health effects of microplastic

In humans, the potential toxicity of microplastics depend on their its size, shape, and polymer type, and the individual’s exposure characteristics, individual health status and level of accumulated chemicals. Microplastic accumulation causes a range of health problems, such as inflammatory responses in tissues, cancer and infertility.

Although there are several studies on the health effects of plastic, Dr Suchana Chavanich, an Associate Professor at the Reef Biology Research Group at Chulalongkorn University, Thailand, admits that knowledge on human health effects of microplastic accumulation is still limited. She observes that while there is strong evidence for the effects of microplastics on marine organisms’ gastrointestinal, endocrine, and circulatory reproductive systems, the evidence is less robust for humans.

Seafood and salt, with a side of microplastic

Humans are exposed to microplastics through air and tap water, as well as food items such as seafood, honey, sugar, beer and salt. Seafood products are among some of the main pathways for microplastic consumption in humans. In Thailand, fish is a major source of protein and per capita annual fish consumption was estimated at around 27.2 kg. As with elsewhere in Southeast Asia, dried and fermented fish products are widely consumed, particularly among low-income groups as a source of protein and seasoning for plain rice.

Recent studies have also shown that that humans ingest several hundred microplastic particles a year solely through the ingestion of salt. Table salts have been increasingly highlighted as an entry pathway of microplastic in humans. Salt is directly consumed through cooking as a condiment but also indirectly consumed as numerous food products use salt in the flavouring and preservative processes. The direct as well as indirect consumption of salt throughout our lives is a long term exposure pathway, additional to exposure from air, water and seafood.

A review of microplastic contamination in commercial salts found that 94% of salt products tested globally, consistently contained three types of microplastics – polyethylene terephthalate, polypropylene, and polyethylene which are some of the most commonly used plastic polymers.

Some studies suggest that microplastics in Asian salts, particularly sea salts (compared to lake and rock or well salts) is high. For instance, a 2018 study of microplastics in 39 salt brands from 21 countries found that concentrations from Asian countries were relatively high compared to brands from other continents; sea salts from Indonesia, China, Thailand and India ranked as the top five for microplastic concentrations.

Microplastics come from the environment as well as packaging processes. Though contamination of microplastics can occur in the processing and packaging stages, the bulk of contamination seems to be from the environment, with studies showing plastic polymers from the marine environment matching those found in table salt.

In Thailand, salt is culturally important. Two main types of salt – sea salt and rock salt – are found in Thailand. Sea salt has been produced historically for medical and culinary uses. In medicine, it is used for treating ailments ranging from food poisoning to inflammation. In food, it is used as preservative, as elsewhere in Southeast Asia, for creating delicacies such as fermented and pickled shrimp and fish, salted fish and fish sauce. Salt is also abundant in Thailand’s much beloved packaged food, such as instant noodles, and its street food.

At the Yung Gleua Baan Leam sea salt farm in Phetchaburi province in the Gulf of Thailand, sea salt farming has been practiced for three generations, and farming practices have changed little throughout the generations. Salt ponds and mounds are formed using wooden tools to prevent rust, and little plastic is used in processing except in the packaging process.

Dr Seelawut Damrongsiri, a researcher at Chulalongkorn University’s Institute of Environmental Research, has been studying microplastic contamination in white, black and flower salt varieties in Samut Sakhon province, also on Thailand’s Gulf. Microplastic was found in all these salts prior to packing, leading Dr Damrongsiri to believe that microplastic contamination is from the land and marine environment.

Thailand’s microplastic regulations

Dr Damrongsiri posits that one possible reason for the ubiquitous presence of microplastics in Thai sea salts is the lack of regulations on microplastics and standardized testing. Though Thailand is party to several international treaties related to marine pollution, including The United Nations Convention on the Law of the Sea (UNCLOS), The International Convention for the Prevention of Pollution from Ships (MARPOL) and the Stockholm Convention on Persistent Organic Pollutants, none address microplastic specifically. However, at the regional level of the Association of Southeast Asian Nations (ASEAN), the Bangkok Declaration in 2019 on Combating Marine Debris in the ASEAN Region noted the urgent need to address the issue of plastics and microplastics.

National laws and policies focus more on microbeads, waste reduction and use of sustainable alternatives. In 2019, Thailand’s Ministry of Public Health announced the banning of the import, production and sale of cosmetic products containing microbeads from January 2020. Also in 2019, the Ministry of Natural Resource and Environment’s Pollution Control Department released the Roadmap on Plastic Waste Management (2018–2030) which identifies banning the use of four types of single-use plastic by 2022. These types are lightweight plastic bags less than 36 microns thick, styrofoam food containers, plastic cups, and plastic straws. The roadmap also aims to replace plastic with more sustainable alternatives by 2030.

At Yung Gleua Baan Leam salt farm, Arada Rodchanabenchakul reflects on the lack of environmental and food safety standards required for the salt she produces from her farm. She told us, “I sell my salt to a middleman, who sells my salt to spas and fish sauce producers. He [the middleman] only checks the salt for colour. Whiter salt is preferred and fetches a higher price.”