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No. 329: Risk assessment of harmful types of plastics in the marine environment

Fauser, P., Bach, L., Daugaard, A.E., Vollertsen, J., Murphy, F., Koski, M., Christensen, A., Andersen, T.J., Scott-Fordsmand, J. & Strand, J. 2019. Risk assessment of harmful types of plastics in the marine environment. Aarhus University, DCE – Danish Centre for Environment and Energy, 74 pp. Scientific Report No. 329. http://dce2.au.dk/pub/SR329.pdf 

Summary

This report presents the results of a risk assessment of chemical additives, monomer residuals and degradation products that are present in plastic (micro) particles in the marine environment. It is not an exhaustive risk assessment of chemical additives but an exemplification of a methodology where known and reported additives representative for significant plastic types and product groups in Denmark are used. The risk approach elucidates the chain from product manufacturing to effects, via fate in the environment and uptake in organisms.

A pioneer study on flocculation of suspensions containing both natural sediment and microplastic (MP) particles has been carried out as part of the project and has shown significant flocculation and no fractionation of the MP particles compared to the other suspended particles. The result of the study is promising and there is a clear need for further studies using a combination of natural particles and MP particles in environmentally relevant concentrations.

The project has supported original research contributions, i.e. sedimentation of dolly ropes and the importance of MP flocculation, which has advanced the understanding and provided computer code that can be further developed and shared between researchers in the future. Both these studies have also given ideas about which aspects of bio-coating processes needs to be further investigated in the future.

To test the effects of potentially toxic MP particles in the marine environment, experiments were conducted where common coastal zooplankton species were exposed to increasing concentrations of new and old car tire particles and filling of artificial turfs (made from old tires), grained to be in a similar size range as the zooplankton prey. The results showed no increase in mortality or decrease in fecundity of zooplankton at or below 10,000 plastic particles per L, irrespective of the plastic type, zooplankton species or food level. As the concentrations of MP in Danish coastal waters are much lower, the short-term effects appear to be unlikely.

A discussion on analytical methods concludes that there is still no consensus on what techniques should be applied for sampling and analysis. A variety of different approaches have been taken, depending on the analytical equipment available, which makes it complicated to estimate field concentrations and to compare MP abundances and composition between areas and over time. Generally, µFTIR is considered to be one of the most widely used methods for identifying MP accurately and quickly. However, there is a definite need to develop standardized methods for monitoring and also to formulate suitable indicators for defining the environmental effects of MP.

The problem of plastic particles of nano-size is also discussed, and finally it is discussed what data and knowledge is needed for improving the risk assessment of MP particles in the marine environment.

Risk Assessment

In collaboration with the plastic industry, seven cases of different polymer types that represent the most significant exposures of MPs and inherent chemicals and thus potential high-risk cases towards marine organisms or eco-
systems, are defined. For each of these cases, product groups with significant use and release to the marine environment are identified:

  • Low-density polyethylene (LDPE): Plastic bags, containers, bottles, tubing, personal care products and bud sticks.
  • Styrene butadiene rubber (SBR): Car tires.
  • Acrylate polymers (acrylics, polyacrylates): Paints for ships and pleasure boats.
  • Polyvinyl chloride (PVC): Cables, cords, linoleum flooring also on ships.
  • Polyurethane (PUR) rigid foam: Building insulation, construction material.
  • Expanded polystyrene (EPS) foam: Building insulation and packaging.
  • Polycarbonate (PC): Construction materials. 

Numerous additives are added intentionally during manufacture including functional additives, such as flame-retardants, plasticizers and biocides. Other additive groups are colorants, fillers and reinforcements. Some additives have been used historically but have been banned, although older products and imported products may still comprise them.

Obtaining information and data on types and amounts of chemical additives used in plastics proved to be complicated. One reason is that all raw materials for Danish plastics converters are imported, and no manufacturing takes place in Denmark. Another significant explanation is lack of transparency due to confidentiality issues. Furthermore, additives are most often present in small amounts <1-2 wt-% and therefore it is not required to include them in safety data sheet for products. The data in this study are compiled from communication with the plastic industry, the scientific literature, manufacturers, reports and web sites.

Also during manufacture, some types of plastics may generate high contents of unreacted residual monomers and oligomers. Some monomers are classified as hazardous. For the considered cases the assessed residual contents are: 0.1wt-% ethylene (LDPE); 0.1wt-% 1,3-butadiene and 0.1wt-% styrene (SBR); 0.01wt-% acrylic acid (acrylic paint); 0.000001wt-% vinyl chloride (PVC); no residual monomers (PUR); 0.5wt-% styrene (EPS); 0.1wt-% bisphenol A (PC).

Risk associated to a given chemical on a MP is not only depending on the environmental concentration and toxicity of the chemical, but also on the specific polymer characteristics that has undergone weathering in the environment. In this study the toxicity of the polymers themselves is not considered, nor is the risk of chemicals sorbed from the surrounding environment (vector effect). For the risk assessment of residual additives, monomers and degradation products the risk assessment procedure for chemicals, outlined in the European Chemicals Agency (ECHA) guidelines that are based on the Technical Guidance Document, is used.

The risk towards marine organism in three trophic levels is calculated, i.e. pelagic/planktonic zooplankton: copepod (Copepoda), benthopelagic fish: Atlantic cod (Gadus morhua) and seabird: northern fulmar (Fulmarus glacialis). For copepod, the exposure is via marine water, for cod via marine water or secondary poisoning and for fulmar via secondary poisoning as top predator and direct ingestion of plastic particles at the sea surface. Predicted Exposure Concentrations (PEC) from maximum measured concentrations of MP in seawater and maximum measured or estimated micro and macro plastic amounts in the stomach/gut are:

·       PEC (MP in marine water): 42 mgMP/m3

·       Cod: 3.5 µgMP/kgbw/day and 700 µgMP/kgfood

·       Fulmar: 1 gplastic/kgbw/day and 3430 µgplastic/kgprey

 

For Predicted No-Effect Concentrations (PNEC), Danish miljøkvalitetskrav (MKK) for other surface waters, according to BEK no 1625 of 19/12/2017, and European Environmental Quality Standard (EQS) values for other surface waters, according to Directive 2013/39/EU, for prioritized substances and certain other pollutants, are used. Additionally, EQS values for secondary poisoning derived in EU 2005 and 2011 dossiers, that form the basis of EU EQS values for prioritized substances in the water framework directive, have been used. In summary, MKK and EQS values for other surface waters are used as PNEC for the pelagic community in marine waters (copepod and cod), and EQS values for food intake (secondary poisoning) are used as PNEC for fulmar. When specific EQS values are available for food ingestion by fish these are used as PNEC, otherwise cod is assessed for the pelagic community.

Realizing the limited available data a fate and exposure scenario to describe the most significant processes and parameters is constructed. Maximum measured and estimated amounts of ingested macro and MP particles in the stomach/gut of fulmar and cod are used as exposure estimates. It is assumed that the ingested plastic consists of only one polymer type at a time. The amount of remaining monomer, additives and degradation products after weathering, i.e. corresponding to the ingested particles, is assumed to be
10 %. Solvents and volatile additives are assumed no longer present. A leachable fraction, estimated to 10% of the remaining chemicals represent the bioavailable fraction.

In the chosen fate-exposure-uptake scenario, some assumptions tend to be worst-case considerations, such as choice of one polymer at a time and use of maximum stomach content, where others have been adjusted to be more realistic, such as estimated leachable and bioavailable fractions.

Seventeen out of approximately 50 identified chemicals have MKK or EU-EQS values, and consequently also PNEC values, and thus they are included in the risk assessment. The risk quotients (RQ) defined as PEC/PNEC are therefore underestimated. The extent of underestimation is however not known. When more than one chemical is present, the RQs for individual chemicals are summed for copepod, cod and fulmar, respectively.

If there is a risk in these conservative scenarios, then more realistic scenarios, with more detailed process descriptions and data, need to be considered.

Potential risk, i.e. RQ > 1, is observed for the pelagic community (copepod and cod) and the flame-retardant pentabromdiphenylether (PeBDE) used in PUR, the biocide tributyltin (TBT) used in PVC and PUR, and the flame-retardant hexabromocyclododecan (HBCD) used in EPS. The highest estimated RQ for fulmar is 0.1 for PeBDE used in PUR.

Production of PeBDE in the EU ceased in 1997. The most common use, accounting for 95-98% of PeBDE since 1999, has been in PUR, which may contain between 10 and 18wt-% of the PeBDE formulation. The use of PeBDE was banned in the EU in 2004 through the Council directive 2003/11/EC relating to restrictions on the marketing and use of certain dangerous substances. Some recycling of articles containing these substances that were produced before introduction of the ban cannot be excluded.

Tributyltins can be present as impurities in mono- and dibutyltin stabilisers up to 1wt-%, but their content has voluntarily been controlled by industry to ≤ 0.67 wt-% (as tin). From July 2010 new products with >0.1wt-% (as tin) are banned.

HBCD is listed in Annex A to the Stockholm Convention with specific exemption for production and use as flame-retardant in EPS and XPS in buildings until August 2017. After this date HBCD in EPS and XPS may still occur in the environment and furthermore significant amounts of HBCD is present in recycled PS packaging.

Another chemical with a relatively high RQ (0.1) for copepod and cod is the softener bis-(2-ethylhexyl)phthalate (DEHP) that is used in PVC.

For the remaining additives, i.e. metals and organic compounds, monomers and methylene dianiline (MDA) a degradation product from methylene diphenyl diisocyanate (MDI) used in PUR, the estimated individual RQs and summed RQs are all below 0.08 indicating an additional margin of safety in relation to the conservative approaches used in this assessment.

This risk assessment of residues from intentionally added chemicals and degradation products in plastics is one of the first steps to unravel the potential risks from MP in the marine environment. Many issues still need to be investigated further in relation to production, fate, uptake and effects. Important data gaps are still not covered need to be covered, and important processes in the environment and the marine organisms should be investigated further. Recommendations for future work are therefore listed in the discussion section of the report.