Relative importance of microplastics as a pathway for the transfer of hydrophobic organic chemicals to marine life

Abstract

It has been hypothesised that, if ingested, plastic debris could act as vector for the transfer of chemical contaminants from seawater to organisms, yet modelling suggest that, in the natural environment, chemical transfer would be negligible compared to other routes of uptake. However, to date, the models have not incorporated consideration of the role of gut surfactants, or the influence of pH or temperature on desorption, whilst experimental work has shown that these factors can enhance desorption of sorbed contaminants several fold. Here, we modelled the transfer of sorbed organic contaminants dichlorodiphenyltrichloroethane (DDT), phenanthrene (Phe) and bis-2-ethylhexyl phthalate (DEHP) from microscopic particles of polyvinylchloride (PVC) and polyethylene (PE) to a benthic invertebrate, a fish and a seabird using a one-compartment model OMEGA (Optimal Modelling for EcotoxicoloGical Applications) with different conditions of pH, temperature and gut surfactants. Environmental concentrations of contaminants at the bottom and the top of published ranges were considered, in combination with ingestion of either 1 or 5% by weight of plastic. For all organisms, the combined intake from food and water was the main route of exposure for Phe, DEHP and DDT with a negligible input from plastic. For the benthic invertebrate, predictions including the presence of contaminated plastic resulted in very small increases in the internal concentrations of DDT and DEHP, while the net change in the transfer of Phe was negligible. While there may be scenarios in which the presence of plastic makes a more important contribution, our modelling study suggests that ingestion of microplastic does not provide a quantitatively important additional pathway for the transfer of adsorbed chemicals from seawater to biota via the gut.

The presence of microplastics in commercial salts from different countries

“…In the case of the latter, MPs have shown the ability to sorb persistent organic pollutants (POPs)45 and subsequently desorb them under simulated gut conditions46. However, recent studies have argued the lower importance of MPs as a vector for translocation of POPs to aquatic biota as compared to other routes like food and water1516. Despite a potentially high concentration of POPs and other contaminants in MPs, the combination of their small particle size and low prevalence indicate that the consumption of sea salt does not appear to be a major route for the contaminant transfer into the human body as compared to other sources like water and food.…”

“…For instance, top European shellfish consumers are expected to ingest up to 11,000 plastic particles per annum14. Microplastics might be of health concern since they have been shown to carry hazardous chemicals1516 and microorganisms17.…”

Microplastics in eviscerated flesh and excised organs of dried fish

“…Subsequently, these chemicals may desorb from the particles into the body of organisms upon ingestion 55 . However, recent studies have shown the intake of POPs by aquatic organisms from water and food exceeded the potential transfer of POPs from ingested MPs 56, 57 . According to the results of this study, the undetectable level of toxic heavy metals on the isolated particles does not support their potential toxicity and the mechanisms whereby MPs cause toxicity are still unclear.…”

Microplastics as a vector of hydrophobic contaminants: Importance of hydrophobic additives

“…A few laboratory studies have revealed that organisms may gain hydrophobic additives such as brominated flame retardants by ingesting plastic particles (e.g., Chua et al 2014;Wardrop et al 2016), whereas modeling studies suggested that the additional uptake via the ingestion of plastic particles would be minimal (Gouin et al 2011;Bakir et al 2016). For nonadditives, plastics are not likely to play important roles because fugacity in plastic particles cannot be greater than that in water.…”

“…However, the observed effects in test organisms would not be environmentally relevant because the dose of plastic particles in laboratory tests is extremely greater than in the field conditions of 100 to 1000 g/km 2 , even in the inner accumulation zones of the ocean gyres (C ozar et al 2014). Modeling studies have revealed that for aquatic organisms, fractional intake via the ingestion of plastic particles would be much smaller than other direct and dietary uptake routes (Gouin et al 2011;Bakir et al 2016). Another aspect that needs to be considered is the direction of chemical flows due to the difference in chemical potential.…”