We
present a generic theoretical model (MICROWEB) that simulates
the transfer of microplastics and hydrophobic organic chemicals (HOC)
in food webs. We implemented the model for an Arctic case comprised
of nine species including Atlantic cod and polar bear as top predator.
We used the model to examine the effect of plastic ingestion on trophic
transfer of microplastics and persistent HOCs (PCBs) and metabolizable
HOCs (PAHs), spanning a wide range of hydrophobicities. In a scenario
where HOCs in plastic and water are in equilibrium, PCBs biomagnify
less when more microplastic is ingested, because PCBs biomagnify less
well from ingested plastic than from regular food. In contrast, PAHs
biomagnify more when more microplastic is ingested, because plastic
reduces the fraction of PAHs available for metabolization. We also
explore nonequilibrium scenarios representative of additives that
are leaching out, as well as sorbing HOCs, quantitatively showing
how the above trends are strengthened and weakened, respectively.
The observed patterns were not very sensitive to modifications in
the structure of the food web. The model can be used as a tool to
assess prospective risks of exposure to microplastics and complex
HOC mixtures for any food web, including those with relevance for
human health.
Human exposure to
microplastic is recognized as a global problem,
but the uncertainty, variability, and lifetime accumulation are unresolved.
We provide a probabilistic lifetime exposure model for children and
adults, which accounts for intake via eight food types and inhalation,
intestinal absorption, biliary excretion, and plastic-associated chemical
exposure via a physiologically based pharmacokinetic submodel. The
model probabilistically simulates microplastic concentrations in the
gut, body tissue, and stool, the latter allowing validation against
empirical data. Rescaling methods were used to ensure comparability
between microplastic abundance data. Microplastic (1–5000 μm)
median intake rates are 553 particles/capita/day (184 ng/capita/day)
and 883 particles/capita/day (583 ng/capita/day) for children and
adults, respectively. This intake can irreversibly accumulate to 8.32
× 10
3
(90% CI, 7.08 × 10
2
–1.91
× 10
6
) particles/capita or 6.4 (90% CI, 0.1–2.31
× 10
3
) ng/capita for children until age 18, and up
to 5.01 × 10
4
(90% CI, 5.25 × 10
3
–9.33
× 10
6
) particles/capita or 40.7 (90% CI, 0.8–9.85
× 10
3
) ng/capita for adults until age 70 in the body
tissue for 1–10 μm particles. Simulated microplastic
concentrations in stool agree with empirical data. Chemical absorption
from food and ingested microplastic of the nine intake media based
on biphasic, reversible, and size-specific sorption kinetics, reveals
that the contribution of microplastics to total chemical intake is
small. The as-yet-unknown contributions of other food types are discussed
in light of future research needs.
The causal links between species traits and bioaccumulation by marine invertebrates are poorly understood. We assessed these links by measuring and modeling polychlorinated biphenyl bioaccumulation by four marine benthic species. Uniformity of exposure was achieved by testing each species in the same aquarium, separated by enclosures, to ensure that the observed variability in bioaccumulation was due to species traits. The relative importance of chemical uptake from pore water or food (organic matter, OM) ingestion was manipulated by using artificial sediment with different OM contents. Biota sediment accumulation factors (BSAFs) ranged from 5 to 318, in the order Nereis virens < Arenicola marina ≈ Macoma balthica < Corophium volutator. Calibration of a kinetic model provided species-specific parameters that represented the key species traits, thus illustrating how models provide an opportunity to read across benthic species with different feeding strategies. Key traits included species-specific differentiation between (1) ingestion rates, (2) ingestion of suspended and settled OM, and (3) elimination rates. The high BSAF values and their concomitant variability across the species challenges approaches for exposure assessment based on pore water concentration analysis and equilibrium partition theory. We propose that combining multienclosure testing and modeling will substantially improve exposure assessment in sediment toxicity tests.
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