Assessment Methods

Ocean plastics retain 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.

1. BFRs

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). They are used to reduce flammability in plastic products such as electronic devices and insulation foams. The additives cover a range of chemicals, including the most commonly used additives in the plastic industry, such as polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane, and tetrabromobisphenol A. Research shows some types of BFRs are not chemically bound to a polymer matrix, causing them to leach into the environment. Some commercial formulations of BFRs, such as 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 were banned in the European Union (EU) in 2004, and the EU also banned deca-BDE for electronic and electrical applications in 2009 (European Commission, 2003; European Council Decision, 2009). Japan banned production and importation of tetra- and hepta-BDEs in 1995 (Covaci et al, 2008).

Several BDEs have also been controlled by the Stockholm Convention since 2004, which prohibits persistent organic pollutants, including deca-, hexa-, hepta-, tetra-, and penta-BDEs.  Southeast Asia and East Asia countries have ratified the convention, including Japan, China, the Republic of Korea, Cambodia, Indonesia, the Lao People’s Democratic Republic, Myanmar, the Philippines, Singapore, and Thailand (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 it does not set allowances for hexa-, hepta-, tetra-, and penta-BDEs, they have to be recycled through an environmentally sound mechanism, 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 the control of relevant stakeholders (Stockholm Convention, 2019c; Stockholm Convention, 2019d).

The EU adopted the Restriction of Hazardous Substances (RoHS) Directive 2002/95/EC, in 2003, which restricts the use of hazardous substances in electrical and electronic equipment, including PBDEs. PBDEs can only be used at 0.1% concentration by weight as they affect the endocrine system (RoHS Guide, 2020). Some Southeast Asian and East Asian countries have adopted a similar approach to PBDEs.

China’s Requirements for Concentration Limits for Certain Restricted Substances in Electrical and Electronic Products SJ/T 11363-2006 states PBDE concentration (deca-BDE not included) in products should not surpass 0.1% by weight. China also has PBDE regulations, 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 controlling the use of PBDEs, they are found in products such as 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 lighting equipment parts 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 being formulated by the Ministry of Industry and the United Nations Development Programme, to reduce or eliminate substances, including PBDEs, which can endanger the environment (Pusat Penelitian Kimia LIPI, 2017).

2. Phthalates or phthalic acid esters (PAEs), found mostly in polyvinyl chloride (PVC), are plasticisers that can take 10%–60% concentration by weight of PVC. As these additives are not bound to a polymer matrix, they can easily leach into the environment during their manufacture, use, and disposal. A big concern is 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, 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) are widely used as antioxidants and plasticisers in plastic production and leach out of plastic bottles. Effluent from wastewater treatment plants is also a major source of NPs. These additives disrupt the endocrine system and can have an adverse impact on human health and the environment. NPs are banned in the EU, and  can be found in seafood, including oysters, mussels, and fish (Hermabessiere et al, 2017).

5. Antioxidants help prevent plastic ageing 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). An oestrogen mimic, an endocrine disruptor, is an artificial hormone that biologically behaves as oestrogen but has a different chemical structure. Excessive amounts of oestrogen in the marine environment can delay the sexual maturity of marine animals, decreasing the size of male reproductive anatomy, and making eggs thinner (UWEC, 2020).

These additives can be found in marine water, sediment, and microplastics. As the final stop of all wastewater, marine water receives huge amounts of additives. PBDEs, di (2-ethylexyl) phthalate (DEHP), and NPs are all detected in marine water. Additives can also be found in sediment affected by anthropogenic discharge through wastewater, atmospheric deposition, and sewage sludge. Plastic additives are found in microplastics as 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. The study showed runoffs from dumping sites during floods and rains are possible drivers that bring additives to surrounding areas, and municipal waste 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 marine fish tissue 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 found oceanic seabirds ingesting plastic debris due to the growing amount of plastic in the ocean. PBDEs were found in the abdominal adipose tissue of the species.