Brian T. Hentschel

Policy: Classify plastic waste as hazardous

Policies for managing plastic debris are outdated and threaten the health of people and wildlife, say Chelsea M. Rochman, Mark Anthony Browne and colleagues.

Long-Term Field Measurement of Sorption of Organic Contaminants to Five Types of Plastic Pellets: Implications for Plastic Marine Debris

Concerns regarding marine plastic pollution and its affinity for chemical pollutants led us to quantify relationships between different types of mass-produced plastic and organic contaminants in an urban bay. At five locations in San Diego Bay, CA, we measured sorption of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) throughout a 12-month period to the five most common types of mass-produced plastic: polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), low-density polyethylene (LDPE), and polypropylene (PP). During this long-term field experiment, sorption rates and concentrations of PCBs and PAHs varied significantly among plastic types and among locations. Our data suggest that for PAHs and PCBs, PET and PVC reach equilibrium in the marine environment much faster than HDPE, LDPE, and PP. Most importantly, concentrations of PAHs and PCBs sorbed to HDPE, LDPE, and PP were consistently much greater than concentrations sorbed to PET and PVC. These data imply that products made from HDPE, LDPE, and PP pose a greater risk than products made from PET and PVC of concentrating these hazardous chemicals onto fragmented plastic debris ingested by marine animals.

INTRASPECIFIC VARIATIONS IN δ13C INDICATE ONTOGENETIC DIET CHANGES IN DEPOSIT-FEEDING POLYCHAETES

Many species change diets during development. Often, these ontogenetic changes are discrete and coincide with metamorphosis (e.g., amphibians), but more gradual niche changes can occur during growth. Identifying nondiscrete changes in diet and understanding their implications at the population and community levels are especially difficult for ecologists who study detritivores and other species that have poorly characterized diets. Theory and several lines of evidence suggest, however, that benthic juveniles of species that deposit feed as adults may be unable to meet their nutritional demands by deposit feeding. To reject the null hypothesis that both juveniles and adults of deposit-feeding species assimilate the same diet and to infer ontogenetic changes in diet, I used stable carbon isotopes as a natural diet tracer. I quantified body-size-dependent variations in the δ13C of four species of tentaculate, surface-deposit-feeding polychaetes: the ampharetid Hobsonia florida and the spionids Pseudopolydora kempi japonica, Polydora cornuta, and Pygospio elegans. In addition to worm tissues, I measured the isotopic compositions of the most likely primary producers at each field site (benthic diatoms, macroalgae, and saltmarsh grasses) to predict the worms’ carbon sources. All species showed significant size-dependent variations in δ13C. Furthermore, populations of P. kempi japonica at two different sandflats had similar ontogenetic trends despite isotopic differences in available foods at each site. Individuals fed a fixed diet in the laboratory, however, did not show significant size-dependent variation in δ13C, leaving ontogenetic changes in diet as the most parsimonious explanation of the field data. Regression analyses indicated that the gradual change in δ13C with body size was nonlinear, with most of the change in δ13C occurring before individuals reach sexual maturity. The complex life cycle of these species, therefore, includes both a radical change in niche when larvae metamorphose to juveniles and a gradual niche shift as benthic juveniles grow. The isotopic data indicate that the smallest juveniles assimilated much of their carbon from benthic diatoms (δ13C ≈ −20‰), while adults assimilated most of their carbon from detritus derived from macroalgae (δ13C ≈ −9‰) or saltmarsh grasses (δ13C ≈ −14‰). Because abundances of benthic diatoms or other high-quality components of sediment are more variable and more likely to be in limiting supply than detritus or bulk sedimentary organics, populations of species that deposit feed as adults may experience food-related recruitment bottlenecks during the juvenile stage.

METAMORPHOSIS OF BARNACLE NAUPLII: EFFECTS OF FOOD VARIABILITY AND A COMPARISON WITH AMPHIBIAN MODELS

Like many animals, barnacles have a complex life cycle with shifts in both diet and habitat. The life cycle of most barnacles has three distinct phases: (1) a planktotrophic nauplius, (2) a non-feeding, planktonic cyprid that subsists on energy reserves, and (3) a benthic juvenile and adult. We conducted a series of experiments to measure the effects of variable food concentration during the naupliar phase on the age, size, and lipid reserves of Balanus glandula cyprids. When food shifted during only the first ∼25% of the naupliar phase (the first three instars), the initial food level did not affect the timing of metamorphosis to the cyprid. Shifts in food that were restricted to the final ∼40% of the naupliar phase (the sixth instar) also did not affect age at metamorphosis. During the intermediate portion of the naupliar phase, enhanced food decreased the age at metamorphosis, while reduced food lengthened the naupliar phase. Cyprid size generally correlated positively with changes in food, but a maxim...

Long-term sorption of metals is similar among plastic types: implications for plastic debris in aquatic environments.

Concerns regarding plastic debris and its ability to accumulate large concentrations of priority pollutants in the aquatic environment led us to quantify relationships between different types of mass-produced plastic and metals in seawater. At three locations in San Diego Bay, we measured the accumulation of nine targeted metals (aluminum, chromium, manganese, iron, cobalt, nickel, zinc, cadmium and lead) sampling at 1, 3, 6, 9 and 12 months, to five plastic types: polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), low-density polyethylene (LDPE), and polypropylene (PP). Accumulation patterns were not consistent over space and time, and in general all types of plastic tended to accumulate similar concentrations of metals. When we did observe significant differences among concentrations of metals at a single sampling period or location in San Diego Bay, we found that HDPE typically accumulated lesser concentrations of metals than the other four polymers. Furthermore, over the 12-month study period, concentrations of all metals increased over time, and chromium, manganese, cobalt, nickel, zinc and lead did not reach saturation on at least one plastic type during the entire 12-month exposure. This suggests that plastic debris may accumulate greater concentrations of metals the longer it remains at sea. Overall, our work shows that a complex mixture of metals, including those listed as priority pollutants by the US EPA (Cd, Ni, Zn and Pb), can be found on plastic debris composed of various plastic types.

Polystyrene plastic: a source and sink for polycyclic aromatic hydrocarbons in the marine environment

Polycyclic aromatic hydrocarbons (PAHs) on virgin polystyrene (PS) and PS marine debris led us to examine PS as a source and sink for PAHs in the marine environment. At two locations in San Diego Bay, we measured sorption of PAHs to PS pellets, sampling at 0, 1, 3, 6, 9, and 12 months. We detected 25 PAHs using a new analytical method with comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry. Several congeners were detected on samples before deployment. After deployment, some concentrations decreased (1,3-dimethylnaphthalene and 2,6-methylnaphthalene), while most increased [2-methylanthracene and all parent PAHs (PPAHs), except fluorene and fluoranthene], suggesting that PS debris is a source and sink for PAHs. When sorbed concentrations of PPAHs on PS are compared to the five most common polymers [polyethylene terephthalate (PET), high-density polyethylene (HDPE), polyvinyl chloride (PVC), low-density polyethylene (LDPE), and polypropylene (PP)], PS sorbed greater concentrations than PP, PET, and PVC, similar to HDPE and LDPE. Most strikingly, at 0 months, PPAHs on PS ranged from 8 to 200 times greater than on PET, HDPE, PVC, LDPE, and PP. The combination of greater PAHs in virgin pellets and large sorption suggests that PS may pose a greater risk of exposure to PAHs upon ingestion.

Complex Life Cycles in a Variable Environment: Predicting When the Timing of Metamorphosis Shifts from Resource Dependent to Developmentally Fixed

To test models of the timing of and size at metamorphosis, researchers manipulate food at several times during the larval phase of an animals complex life cycle. Data from diverse taxa show that the age at metamorphosis becomes resource independent (i.e., fixed) at some point during the larval phase. Although existing models have been modified to incorporate a fixed rate of development, none predicts when phenotypic plasticity in metamorphic timing is lost. A graphical model is presented that extends knowledge of a genotypes optimal age and size at metamorphosis in different environments in which resources remain constant throughout the larval phase (i.e., the genotypes reaction norm) to predict when development rate becomes fixed in response to resource variability during the larval phase. Model predictions concur with data from food‐switching experiments on anuran tadpoles and barnacle nauplii. As interest in the timing of and size at metamorphosis expands from well‐studied taxa (e.g., amphibians) to the many others that have complex life cycles, the predictive model provides a useful tool to design and improve experiments.

Ontogenetic changes in particle-size selection by deposit-feeding spionid polychaetes: the influence of palp size on particle contact

Scaling arguments suggest that juveniles of species that deposit feed as adults must ingest relatively higher quality diets to compensate for a digestive constraint imposed by small body (and gut) size. Understanding how and why particle-size selection varies ontogenetically can provide clues to the relative quality of forage juveniles obtain. Particle selection by a tentacle or palp feeder can be viewed as the net result of particle contact, collection, and post-collection rejection. A geometrical model of particle contact that includes effects due to palp size predicts that thinner palps and hence smaller worms are biased toward contacting larger particles. The models prediction was tested using adhesive-coated palp mimics (monofilament line) of varying diameters spanning the range of actual palps to contact and collect particles from a mixture of two sizes of glass beads (16 and 88 μm dia). Results were consistent with the contact models prediction: thinner palp mimics collected a lower proportion of small beads (higher proportion of large beads). Intraspecific variations in particle-size selection due to body, and palp size were determined for Pseudopolydora kempi japonica Imajima and Hartman, Polydora ligni Webster, Boccardia proboscidea Hattman, and Pygospio elegans Claparede by conducting laboratory feeding experiments with the same mixture of glass beads used with mimics. P. kempi japonica results were consistent with the contact model and the palp-mimic experiment. B. proboscidea and P. elegans showed no significant variation with body size. Polydora ligni showed a negative relationship between particle size and body (and palp) size; insufficient mouth size of small juveniles is a likely explanation. Assuming that food value (per unit volume of ingested material of sedimentary detritus is negatively correlated with particle size, results suggest that deposit-feeding juveniles cannot increase diet quality without post-contact sorting mechanisms that probably increase handling costs-perhaps leading to macrophagous evaluation of individual particles based more on nutritional content than on mechanical properties like size. Increasing the time spent suspension feeding relative to deposit feeding is another likely means for juvenile spionids to increase diet quality and perhaps overcome the combined digestive and deposit-feeding constraints imposed by small gut and palp size.

Combined effects of water flow and copper concentration on the feeding behavior, growth rate, and accumulation of copper in tissue of the infaunal polychaete Polydora cornuta

We performed an experiment in a laboratory flume to test the effects of water flow speed and the concentration of aqueaous copper on the feeding behavior, growth rate, and accumulation of copper in the tissues of juvenile polychaetes Polydora cornuta. The experiment included two flow speeds (6 or 15 cm/s) and two concentrations of added copper (0 or 85 μg/L). Worms grew significantly faster in the faster flow and in the lower copper concentration. In the slower flow, the total time worms spent feeding decreased significantly as copper concentration increased, but copper did not significantly affect the time worms spent feeding in the faster flow. Across all treatments, there was a significant, positive relationship between the time individuals spent feeding and their relative growth rate. Worms were observed suspension feeding significantly more often in the faster flow and deposit feeding significantly more often in the slower flow, but copper concentration did not affect the proportion of time spent in either feeding mode. The addition of 85 μg/L copper significantly increased copper accumulation in P. cornuta tissue, but the accumulation did not differ significantly due to flow speed. There was a significant interaction between copper and flow; the magnitude of the difference in copper accumulation between the 0 and 85 μg/L treatments was greater in the faster flow than in the slower flow. In slow flows that favor deposit feeding, worms grow slowly and accumulate less copper in their tissue than in faster flows that favor suspension feeding and faster growth.