Source: Andrady and Rajapakse (2017).
Plastic in oceans retains additives, which are then directly transferred to marine organisms through prey ingestion. Indirect toxicity results when additives not chemically bound to the plastic are released into the environment and become available to organisms (Hermabessiere et al., 2017).
The most common additives found in marine debris are brominated flame retardants (BFRs) , phthalates, nonylphenols, bisphenol A (BPA), and antioxidants.
Generally, BFRs are potential endocrine disruptors. Organisms exposed to endocrine disruptors will suffer in multiple developmental, reproductive, neurological, immune, and metabolic diseases (Ingre-Khans, Ågerstrand, and Rudén, 2017). BFRs are used in plastic products such as electronic devices and insulation foams to reduce flammability. The additives cover a range of chemicals, including the most commonly used additives in plastic industry, such as polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane, and tetrabromobisphenol A. Research shows that some types of BFRs are not chemically bound to polymer matrix, thus causing them to leach into the environment. Some commercial formulations of BFRs, called penta-, octa-, and deca-brominated diphenyl ethers (BDEs), are ubiquitous, harmful, stable, and bioaccumulate in the environment, with detrimental impacts on human health. Penta- and octa-BDEs have been banned in the European Union (EU) since 2004. The EU also banned deca-BDE for electronic and electrical applications in 2009 (European Commission, 2003; European Council Decision, 2009). Japan has banned production and importation of tetra- and hepta-BDEs since 1995 (Covaci et al., 2008).
Besides being regulated under the European Council Decision in 2009, several types of BDEs have also been controlled by the Stockholm Convention since 2004. The convention prohibits persistent organic pollutants, which include deca-, hexa-, hepta-, tetra-, and penta-BDEs. Many countries in Southeast Asia and East Asia, including Japan, China, the Republic of Korea, Cambodia, Indonesia, the Lao People’s Democratic Republic, Myanmar, the Philippines, Singapore, and Thailand, have ratified the convention (Stockholm Convention, 2019a). Under the regulation, deca-BDEs in plastic housing and parts used for heating home appliances are allowed at concentrations lower than 10% by weight (Stockholm Convention, 2019b). Although the convention does not set allowances for hexa-, hepta-, tetra-, and penta-BDEs, these have to be recycled through an environmentally sound mechanism, they are not allowed to be exported if their concentrations exceed the standard in the territory of the involved party, and their use must be under control of relevant stakeholders (Stockholm Convention, 2019c; Stockholm Convention, 2019d).
In 2003, the EU adopted the Restriction of Hazardous Substances (RoHS) Directive 2002/95/EC, which restricts the use of hazardous substances in electrical and electronic equipment. PBDEs are amongst the prohibited substances. The directive notes that PBDEs can be used only at 0.1% concentration by weight since they affect the endocrine system (RoHS Guide, 2020). Some Southeast Asian and East Asian countries have adopted a similar approach regarding PBDEs. For instance, China’s Requirements for Concentration Limits for Certain Restricted Substances in Electrical and Electronic Products SJ/T 11363-2006 states that PBDE concentration (deca-BDE not included) in products should not surpass 0.1% by weight. In general, China has regulations on PBDEs, such as the Ordinance on Management of Pollution and Control of Pollution from Electronic Information Products in 2007 and the Administrative Measures on Pollution Prevention of Waste from Electrical and Electronic Equipment in 2008 (revised in 2016) (Ni et al., 2012; Chem Safety Pro, 2019). Weak enforcement of those regulations, however, remains an issue (Ni et al., 2012). Viet Nam and Singapore allow the use of PBDEs with as much as 0.1% concentration by weight in electric or electronic products (Government of Viet Nam, 2011; Government of Singapore, 2020). As Thailand has no strong legal frameworks that control the use of PBDEs, they are found in some products, including electronics, furniture, and car seats. However, some types of BDEs (47, 99, 153, 175, and 183) will be added to the Thailand Hazardous Substances List, which is annexed to the Notification of Ministry of Industry on List of Hazardous Substances (No. 4) (Muenhor and Harrad, 2018). Malaysia also prohibits the use of PBDEs in parts of lighting equipment based on MS 2237:2009, which restricts certain hazardous substances in electrical and electronic devices (SCP Malaysia, 2014). In Indonesia, a recommendation on industrial waste management is still being formulated by the Ministry of Industry and the United Nations Development Programme. This recommendation will aim to reduce or eliminate substances, including PBDEs, that can endanger the environment (Pusat Penelitian Kimia LIPI, 2017).
Phthalates or phthalic acid esters (PAEs), found mostly in polyvinyl chloride (PVC), are plasticisers that can take 10%–60% concentration by weight of PVC. Since these additives are not bounded to polymer matrix, they can easily leach into the environment during their manufacture, use, and disposal. A big concern is that phthalates can serve as endocrine disruptors even in small concentrations (Hermabessiere et al., 2017).
3. Bisphenol A (BPA)
As one of the most commonly and globally produced chemicals, BPA is primarily used as monomer of the main component of the lining of aluminium cans. Humans are exposed to BPA once it is released from food and drink packaging. Like phthalates, BPA is a significant endocrine disruptor. Other types of bisphenol, including bisphenol B, F, and S, may also pose threats to the environment (Hermabessiere et al., 2017).
4. Nonylphenols (NPs)
NPs are widely used as antioxidants and plasticisers in plastic production. They leach out of plastic bottles. Effluents from wastewater treatment plants are also a major source of NPs. These additives disrupt the endocrine system and can have adverse impacts on human health and the environment. NPs are banned in the EU. NPs can be found in seafood, including oysters, mussels, and fish (Hermabessiere et al., 2017).
Antioxidants help prevent ageing of plastic and delay oxidation but can leach out of plastic packaging and into food. The use of antioxidants in plastic can be harmful because they are oestrogen mimics (Hermabessiere et al., 2017). One of the classes of endocrine disruptors, an oestrogen mimic is an artificial hormone that biologically behaves as oestrogen but has a different chemical structure. Excessive amounts of estrogen in the marine environment can impact marine animals by delaying their sexual maturity, decreasing the size of male reproductive anatomy, and making eggs thinner (UWEC, 2020).
These additives can be found in marine water, sediment, and microplastic. As the final stop of all wastewater, marine water receives huge volumes of additives. PBDEs, di (2-ethylexyl) phthalate (DEHP), and NP are mostly detected in marine water. Additives can also be found in sediments affected by anthropogenic discharge through wastewater, atmospheric deposition, and sewage sludge. Plastic additives are found in microplastics since they are added in the manufacture of polyethylene and polypropylene (Hermabessiere et al., 2017).
Several studies on the chemical impacts of plastic have been conducted in Southeast Asian and East Asian countries. A study in the Mekong River Delta in Viet Nam revealed PBDE contamination in catfish, posing risks to people who eat them. This study showed that runoffs from dumping sites during floods and rains are the possible drivers that bring additives to surrounding areas. In this case, municipal wastes in dumping sites, consisting of household goods and electrical equipment, might contain PBDEs. Research in informal e-waste recycling sites in Viet Nam found high PBDE contamination in surrounding sediment and in fish, particularly mud carp. This was attributed to the high level of PBDEs in plastic parts in obsolete electronic equipment in e-waste recycling sites. Liu et al (2011) discovered PBDE contamination in tissues of marine fish from the South China Sea, the Bohai Sea, the East China Sea, and the Yellow Sea, while Ilyas et al. (2013) indicated that a high level of PBDEs was observed in municipal dumpsites. Seabirds are also vulnerable to the impacts of chemicals in plastic. A study in the northern Pacific Ocean discovered oceanic seabirds ingesting plastic debris due to the growing amount of plastic entering the ocean. PBDEs were found in the abdominal adipose tissue of the species.
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