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Assessing microplastic exposure of large marine filter-feeders
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Researchers analyzed whale scat to estimate microplastic exposure in baleen whales feeding in coastal New Zealand waters. Using stochastic simulation modeling, they estimated whales ingest over 3.4 million microplastics per day, a figure four orders of magnitude higher than would be predicted from surface water measurements alone. The study suggests that trophic transfer through prey is the dominant exposure route for large filter-feeding marine animals, not direct environmental ingestion.
Large filter-feeding animals are potential sentinels for understanding the extent of microplastic pollution, as their mode of foraging and prey mean they are continuously sampling the environment. However, there is considerable uncertainty about the total and mode of exposure (environmental vs trophic). Here, we explore microplastic exposure and ingestion by baleen whales feeding year-round in coastal Auckland waters, New Zealand. Plastic and DNA were extracted concurrently from whale scat, with 32 ± 24 (mean ± SD, n = 21) microplastics per 6 g scat sample detected. Using a novel stochastic simulation modeling incorporating new and previously published DNA diet information, we extrapolate this to total microplastic exposure levels of 24,028 (95% CI: 2119, 69,270) microplastics per mouthful of prey, or 3,408,002 microplastics (95% CI: 295,810, 10,031,370) per day, substantially higher than previous estimates for large filter-feeding animals. Critically, we find that the total exposure is four orders of magnitude more than expected from microplastic measurements of local coastal surface waters. This suggests that trophic transfer, rather than environmental exposure, is the predominant mode of exposure of large filter feeders for microplastic pollution. Measuring plastic concentration from the environment alone significantly underestimates exposure levels, an important consideration for future risk assessment studies.
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Are baleen whales exposed to the threat of microplastics? A case study of the Mediterranean fin whale (Balaenoptera physalus)
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This case study estimated how many microplastics Mediterranean fin whales and basking sharks might ingest through filter feeding, using feeding rate data and measured microplastic concentrations. The study raised concern that large filter feeders accumulate significant plastic loads and that the associated chemical burden from sorbed pollutants may pose health risks to these protected species.
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Researchers measured microplastic loads in the zooplankton prey and fecal matter of gray whales feeding off the Oregon coast, producing the first empirically-based estimates of daily microplastic consumption by a baleen whale. All zooplankton species examined contained microplastics, averaging four particles per gram, mostly tiny fibers. Based on these measurements, the study estimates that pregnant and lactating gray whales may consume between 6.5 and 21 million microplastic particles per day through their food alone.
Ingestion of microplastics by fish and other prey organisms of cetaceans, exemplified for two large baleen whale species
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Researchers reviewed microplastic contamination in the prey species of minke and sei whales, finding microplastics were widespread in krill, fish, and other whale food. Since cetaceans consume large quantities of these prey, they are likely ingesting significant amounts of microplastics indirectly through their diet.
Large filter feeding marine organisms as indicators of microplastic in the pelagic environment: The case studies of the Mediterranean basking shark (Cetorhinus maximus) and fin whale (Balaenoptera physalus)
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This study investigated whether baleen whales and basking sharks — large filter feeders — ingest microplastics in the Mediterranean and found evidence that both species are exposed to plastic contamination through their filtration feeding behavior. The authors used feeding ecology modeling to estimate plastic ingestion rates and identify associated toxicological risks.
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