Plastic on the plate
Assessing the risks to human health from marine plastic
is a complex process and there is still a lot of debate
over the quantity of plastic being ingested from seafood
and whether it has the potential to affect the health of
consumers. Consumption of filter feeding invertebrates,
such as mussels and oysters, appears the most likely
route for human consumption of microplastics, because
people eat the whole organism including the gut. It has
been shown that mussels can retain some plastic in their
circularity system for over 48 days (Browne et al., 2008). It
is estimated that high consumers of mussels in Belgium
could ingest up to 11,000 pieces of microplastic in a year
(an average of 90 particles per meal over 122 meals; Van
Cauwenberghe and Janssen, 2014). The presence of
microplastic particles in seafood could pose a human health
risk (Van Cauwenberghe and Janssen 2014; Bouwmeester
et al., 2015), especially if, following ingestion, the particles
move from the digestive system to come into contact with
organs and tissues. However, there is currently no evidence
of ingested microplastics moving from the gut into other
parts of the human body (Galloway, 2015).
In contrast to microplastics, it is thought that nano-sized
material (less than 100 nm) may be more readily absorbed
through the digestive system into the body. Evidence for
this comes largely from studies investigating the ingestion
of engineered nanospheres as a method of drug delivery,
where they have been seen to cross the gut barrier and
enter the circulatory system (e.g. Hussain et al., 2001).
Bouwmeester et al. (2015) reviewed laboratory studies that
demonstrate uptake of nanoparticles bymarine organisms,
including mussels and scallops. However, they conclude
that there is insufficient evidence to determine whether
the absorbed nanoparticles can go beyond the circulatory
system and enter cells. There is also some debate about the
extent of nanoplastics in the ocean. It has been suggested
that they are produced from the fragmentation of larger
plastic particles, helped by both physical and microbial
processes (Cozar et al., 2014 and Lawet al., 2014). At present
it is technically difficult to detect nanoparticles in tissue or
in the marine environment, so new detection methods are
required to determine the extent and fate of these particles
(Bouwmeester et al. 2015).
What about the chemicals?
In addition to the potential physical effects of ingesting
plastic, there may also be associated chemical toxicity.
Marine debris has been shown to contain a cocktail of
chemicals including monomers and additives like flame
retardants, antioxidants, UV-stabilizers and plasticizers.
There is research that indicates that some of these
chemicals can act as endocrine disruptors in humans
(reviewed in Talsness et al., 2009). Chemicals of particular
concern are phthalates and bisphenol A (BPA), which
animal studies suggest may impair reproductive function
and be carcinogenic, even at very low doses (Meeker et
al., 2009; vom Saal et al., 2007). However, even though
phthalates and BPA have been in commercial use for over
50 years, studies into the effects on humans are limited.
Several studies have explored possible associations
between phthalates and conditions such as altered
semen quality and shortened gestation, although data
are limited and the results inconclusive (Hauser and
Calafat, 2005). A hazard analysis of plastic polymers
identified polyurethanes (used in hard plastic parts and
There is growing concern that toxic chemicals from plastic debris, especially micro-
and nanoplastics, are making their way into the food chain. But are they harmful?
Anthropogenic marine debris has been observed throughout the ocean, from beaches
and shallow coral reefs to the deep sea. Plastic particles have been found in hundreds
of species of marine organisms, including many species of fish and shellfish sold
for human consumption. A recent study found plastic in one out of every four fish
purchased from markets in the United States and Indonesia (Rochman et al., 2015).
Globally, average per capita fish consumption is nearly 20 kg per year and seafood
equates to nearly 17 per cent of the world’s protein consumption (FAO, 2014), so there
is a potential pathway for human exposure to plastic.
Plastic in the food chain –
a threat to human health?