Microplastics in the marine environment and possible risks to human health

Abstract

Microplastics are contaminants of emerging concern, defined as solid particles < 5 mm. First found in marine waters, varying concentrations of microplastics have also been reported from other marine and terrestrial compartments. Edible marine resources for human consumption have not been spared. While a great deal of work has been published in recent years, some of the most basic information to assess the potential risks of microplastics to human health is still missing. Such assessments are further hindered by using a plethora of methods in microplastics research and data quality issues abound leading to issues with interstudy comparability and uncertainty of results. Therefore, this PhD aimed to provide some of this basic information by assessing microplastic concentrations in marine foodstuff directly and indirectly consumed by humans. In addition, great care was taken to produce results that could be compared with other studies and establish optimised methods wherever possible with the need for microplastic result descriptions to single-digit micrometre scale in mind. My results demonstrate that microplastics are present in food-grade European sea salts and fishmeal used as feed for other organisms in the human food chain. Based on assumed absorption rates and consumer choices, I calculate annual human exposure through sea salt and how much may be recirculating to the environment. Similarly, I estimate the exposure potential of microplastics in fishmeal to the supply chain and, conversely, augmentation of existing environmental concentrations. Using an already published method for microplastics in sea salt I show that interstudy comparability is hindered through focus on particle extractions well above single-digit micrometre particle size and incomplete filtrations. In addition, I uncover the general lack of detailed method descriptions of polymer identification steps. I tested the use of NaCl density separation to extract microplastics from fishmeal, greatly increasing the target size from 150 µm to 50 µm. Both data chapters indicate that processing of edible marine resources increases microplastic concentrations likely through contamination entering at some point through the harvesting and production steps. I further compare existing digestion protocols for their suitability—mainly guided by the need of filtration to single-digit particles to aid the assessment of risks to humans—and optimised an existing digestion protocol for bivalves. This investigative work adds to the necessary groundwork for toxicological risk assessments by providing microplastic mass and concentrations in food sources from the marine environment and showing that handling of edible food sources seems to increase microplastic loads in products. It also highlights that method harmonisation is needed for interstudy comparability for every step of the analytical work and the existing lack of result reporting to single-digit micrometre scale to aid human risk assessments. If microplastics pose a risk to human health remains to be seen, but a basic requirement for subsequent work is the production of data of good quality, including detailed information of how microplastics were identified, their sizes and particle mass estimates.

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Identifiers

ORCID for Christina Johanna Thiele: orcid.org/0000-0002-3160-1189

ORCID for Andrea Russell: orcid.org/0000-0002-8382-6443

ORCID for Antony Jensen: orcid.org/0000-0002-8924-1198

ORCID for David Coggon: orcid.org/0000-0003-1930-3987

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