Characterization of Metal Pulsed Exposure to Aquatic Organisms with Post-Exposure Monitoring: Implications for Stormwater Exposure Assessment.

Freshwater organisms are often exposed to contaminants such as heavy metals from stormwater discharges, which are dependent on rainfall duration and intensity. Therefore, standardized (48- or 96-h) continuous exposure methods developed for whole effluent toxicity (WET) testing might not always accurately convey the effects of stormwater and runoff contaminants. The present study characterized the acute toxicity of copper (Cu), zinc (Zn), and cadmium (Cd) to freshwater amphipods (Hyalella azteca) and cadmium (Cd) to water fleas (Ceriodaphnia dubia) using a modified exposure design that integrated relevant pulsed durations and included post-exposure monitoring. Less than 24-h-old C. dubia and 7 to 8-day-old H. azteca were exposed to water spiked with Cu, Zn, or Cd using 6-, 12-, 26-, or 96-h durations under standard laboratory conditions and monitored for cumulative mortality and reproduction (C. dubia only). Lethal effect (LC10s, LC25s, LC50s) and reproductive effect (EC25s, EC50s) were determined based on either mortality or reproduction of organisms at the end of each pulse (6, 12, or 26 h) and at the end of their respective tests (96 h). For all metals exposed to each organism, acute toxicity was found to be highest for the (96 h) continuous exposures. For pulsed exposures, mortality continued to increase following transfer to clean water for post-exposure monitoring. These results indicate a latent effect of Cu, Zn, and Cd to H. azteca and Cd to C. dubia. The present study concluded that using the continuous (48- or 96-h) WET exposure method overestimates the effects of stormwater and runoff contaminants. However, pulsed exposures without post-exposure monitoring also underestimate the toxicity of contaminants. The proposed pulsed exposure design provides a compromise that is more realistic than current WET methods to assess impacts from episodic events and accounts for potential latent effects that may be overlooked without monitoring post-exposure. Environ Toxicol Chem 2022;41:2488-2499. © 2022 SETAC.

Pulsed exposure toxicity testing: Baseline evaluations and considerations using copper and zinc with two marine species.

Methods to assess environmental impacts from episodic discharges on receiving water bodies need a more environmentally relevant and scientifically defensible toxicity test design. Many permittees are regularly required to conduct 96-h toxicity tests on discharges associated with events that are generally less than 24 h in duration. Current standardized methods do not adequately reflect these episodic discharge conditions at either the point of compliance nor as it mixes with the receiving environment. In order to evaluate more representative biological effects, an alternative toxicity approach is described incorporating pulsed exposures of effluents and subsequent transfer of test organisms to clean water for the remainder of the test. This pulsed exposure protocol incorporates a slight modification to USEPA Whole Effluent Toxicity (WET) chronic and acute methods for two marine species, purple sea urchin embryos, Strongylocentrotus purpuratus, and juvenile mysid shrimp Americamysis bahia. Tests were performed with toxicants using standard static (96 h) and pulsed (6, 12, and 26 h) exposures. Following pulsed exposures, organisms were transferred to uncontaminated seawater for the remainder of the 96-h test period. Results for these species and endpoints indicated that the sensitivity of these species to copper and zinc were up to two orders of magnitude greater using standard continuous exposures compared to shorter pulsed exposures. Additional considerations assessed included timing of the onset of a pulse and latent effects following an exposure. This modified approach requires minimal modification to current standard methods and increases the realism to more accurately assess toxic effects resulting from episodic discharges.

Aquatic toxicity evaluations of PFOS and PFOA for five standard marine endpoints.

Per- and poly-fluoroalkyl substances (PFAS) are emerging contaminants that are coming under increasing scrutiny. Currently, there is a paucity of effects data for marine aquatic life, limiting the assessment of ecological risks and compliance with water quality policies. In the present study, the toxicity of perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) to four standard marine laboratory toxicity testing species, encompassing five endpoints, were evaluated: 1) 96-h embryo-larval normal development for the purple sea urchin (Strongylocentrotus purpuratus); 2) 48-h embryo-larval normal development and normal survival for the Mediterranean mussel (Mytilus galloprovincialis); 3) 96-h survival of opossum shrimp (Americamysis bahia); and 4) 24-h light output for the bioluminescent dinoflagellate Pyrocystis lunula. All species were tested using standard United States Environmental Protection Agency (USEPA) and/or American Society for Testing and Materials (ASTM) International protocols. For PFOS and PFOA, the order of species sensitivity, starting with the most sensitive, was M. galloprovincialis, S. purpuratus, P. lunula, and A. bahia. The range of median lethal or median effect concentrations for PFOS (1.1-5.1 mg L-1) and PFOA (10-24 mg L-1) are comparable to the relatively few toxicity effect values available for marine species. In addition to providing effects data for PFOA and PFOS, this study indicates these species and endpoints are sensitive to PFAS such that their use will be appropriate for deriving toxicity data with other PFAS in marine ecosystems.

Assessing Biota Accumulation Due to Contamination of Sediments by Storm Water Heavy Metals.

Evaluating sediment recontamination due to storm water discharges is important when evaluating the long-term effectiveness of sediment remediation efforts at reducing biological impacts. The bioaccumulation of the heavy metals zinc, nickel, copper, cadmium, mercury, and lead and the metalloid arsenic in a clam (Macoma nasuta) was studied in surficial sediments before and after storm water inputs from Paleta Creek, California, USA, during wet seasons in 2015 to 2016 and 2016 to 2017. The bioaccumulation was compared with bulk sediment concentrations and porewater concentrations measured by diffusion gradient in thin film devices. Significant reductions in biota accumulation and porewater concentrations were observed in samples collected after storm seasons compared with before storm seasons despite bulk sediment concentrations remaining the same or increasing. This was apparently the result of the deposition of storm water contaminants in low bioavailable forms. The bioaccumulation of all the measured contaminants showed a positive significant correlation with porewater concentrations (p < 0.1, α = 0.1) and weak or no correlations with bulk sediment concentration. In conclusion, observed bulk sediment recontamination due to storm water should not be assumed to lead directly to greater biota accumulation without bioavailability assessment. Environ Toxicol Chem 2020;39:2475-2484. © 2020 SETAC.

Assessing sediment recontamination from metals in stormwater.

Recontamination of sediments by stormwater is a major concern when evaluating the potential effectiveness of sediment remediation. Stormwater and sediment sampling were conducted in a mixed-use watershed at Paleta Creek in San Diego, CA to evaluate methods for assessing sediment recontamination by metals. Size-segregated stormwater contaminant loads with simultaneous receiving water and sediment measurements were used to identify dominant sources and contaminants with respect to their impact on sediment recontamination. Most of the stormwater contaminant loads of Cd, Cu, Pb, and Zn were associated with residential and highway sources from the upstream portions of the watershed and As, Ni and Hg were more significantly influenced by the downstream area of the watershed. Cd was strongly associated with large particles (>63 µm) and observed to settle in near shore areas with some attenuation due to mixing and dilution. Cu, in contrast, was associated more with the filtered fraction (<0.45 µm) and clay fraction (0.45-5 µm), resulting in less near shore sediment recontamination. Depositing sediment and other metals, particularly Cu and Hg, exhibited greater accumulation in settling traps than could be attributed to stormwater loads indicating the importance of other sources or resuspension of bay sediments on surficial sediment concentrations. Pb, Zn, Ni, and As showed influences of both stormwater and other sources. The study showed that measurement of size-segregated stormwater contaminant mass and concentrations combined with simultaneous measurements of deposition in sediment traps could differentiate between recontamination by stormwater and that of other sources.

Estimates of environmental loading from copper alloy materials.

Metal release rates were measured from four different copper alloy-based materials used by the aquaculture industry: copper sheet machined into a diamond mesh, copper alloy mesh (CAM), silicon bronze welded wire mesh, and copper sheeting, and compared with conventional nylon aquaculture net treated with a cuprous oxide antifouling (AF) coating. Release rates were measured in situ in San Diego Bay using a Navy-developed Dome enclosure system at nine different time points over one year. As expected, copper was the predominant metal released, followed by zinc and nickel, which were fractional components of the materials tested. Release rates followed a temporal trend similar to those observed with copper AF coatings applied to vessel hulls: an initial spike in copper release was followed by a decline to an asymptotic low. Leachate toxicity was consistent with prior studies and was directly related to the metal concentrations, indicating the alloys tested had no additional toxicity above pure metals.

Seasonal Toxicity Observed with Amphipods (Eohaustorius estuarius) at Paleta Creek, San Diego Bay, USA.

To assess potential impacts on receiving systems, associated with storm water contaminants, laboratory 10-d amphipod (Eohaustorius estuarius) survival toxicity tests were performed using intact sediment cores collected from Paleta Creek (San Diego Bay, CA, USA) on 5 occasions between 2015 and 2017. The approach included deposition-associated sediment particles collected from sediment traps placed at each of 4 locations during the 2015 to 2016 wet seasons. The bioassays demonstrated wet season toxicity, especially closest to the creek mouth, and greater mortality associated with particles deposited in the wet season compared with dry season samples. Grain size analysis of sediment trap material indicated coarser sediment at the mouth of the creek and finer sediment in the outer depositional areas. Contaminant concentrations of metals (Cd, Cu, Hg, Ni, Pb, and Zn) and organic compounds (polycyclic aromatic hydrocarbons [PAHs], polychlorinated biphenyls [PCBs], and pesticides) were quantified to assess possible causes of toxicity. Contaminant concentrations were determined in the top 5 cm of sediment and porewater (using passive samplers). Whereas metals, PAHs, and PCBs were rarely detected at sufficient concentrations to elicit a response, pyrethroid pesticides were highly correlated with amphipod toxicity. Summing individual pyrethroid constituents using a toxic unit approach suggested that toxicity to E. estuarius could be associated with pyrethroids. This unique test design allowed delineation of spatial and temporal differences in toxicity, suggesting that storm water discharge from Paleta Creek may be the source of seasonal toxicity. Environ Toxicol Chem 2019;39:229-239. © 2019 SETAC.

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.

Preliminary ecotoxicity assessment of new generation alternative fuels in seawater.

The United States Navy (USN) is currently demonstrating the viability of environmentally sustainable alternative fuels to power its fleet comprised of aircraft and ships. As with any fuel used in a maritime setting, there is potential for introduction into the environment through transport, storage, and spills. However, while alternative fuels are often presumed to be eco-friendly relative to conventional petroleum-based fuels, their environmental fate and effects on marine environments are essentially unknown. Here, standard laboratory-based toxicity experiments were conducted for two alternative fuels, jet fuel derived from Camelina sativa (wild flax) seeds (HRJ5) and diesel fuel derived from algae (HRD76), and two conventional counterparts, jet fuel (JP5) and ship diesel (F76). Initial toxicity tests performed on water-accommodated fractions (WAF) from neat fuels partitioned into seawater, using four standard marine species in acute and chronic/sublethal tests, indicate that the alternative fuels are significantly less toxic to marine organisms.