Impact of dispersant on early life stages of the water flea Daphnia magna and the eastern oyster Crassostrea virginica

Sublethal Effects of Crude Oil and Chemical Dispersants on Multiple Life History Stages of the Eastern Oyster, Crassostrea virginica

The eastern oyster Crassostrea virginica is an ecologically and economically important species that is vulnerable to oil pollution. We assessed sublethal effects of soluble fractions of crude oil alone (WAF) and crude oil in combination with Corexit 9500 dispersant (CEWAF) on oysters at three life history stages. Veliger swimming, pediveliger settlement, and adult clearance rates were quantified after 24 h exposures to the contaminants. Veliger swimming speeds were not significantly impacted by 24 h exposures to WAF or CEWAF. A larger proportion of veligers were inactive following WAF and CEWAF exposure as compared to the control, but the effect was greater for pediveligers, and pediveliger settlement in the highest concentration CEWAF treatment decreased by 50% compared to controls. Thus, pediveligers may be particularly vulnerable to oil exposure. In the adults, we found significant clearance rates reductions that persisted 33 days after acute exposure to CEWAF. Knowledge of sublethal effects of oil and dispersant at multiple life history stages aids understanding of how this important species will respond to an oil spill.

Identifying alternative solvents for C60 manufacturing using singular and combined toxicity assessments

Linseed oil, olive oil, and sunflower oil were selected based on green chemistry principles and C₆₀ solubility as alternative solvents to replace 1,2,4-trimethylbenzene (TMB) for C₆₀ manufacturing. Singular acute toxicity experiments of C₆₀ and the four solvents was performed using Daphnia magna to identify the solvent with the lowest toxicity and estimate the toxicity of C₆₀. The EC₅₀ for C₆₀ was estimated to be higher than 176 ppm. The toxicity of the solvents increased from sunflower oil to olive oil, linseed oil, and TMB. Combined toxicity tests were conducted to investigate the interaction between C₆₀ and the solvent since essential oils can be nanocarriers and facilitate the transport of C₆₀ into the cell membranes, which would increase its toxicity. Various concentrations of C₆₀ (0, 11, 22, 44, 88, and 176 mg/L) were mixed with solvents at their EC₅₀ concentrations. The toxicity of linseed oil increased with increasing C₆₀ concentrations. For olive and sunflower oil, the toxicity was lowered with low concentrations of C₆₀. Olive oil was determined to be a suitable solvent for C₆₀ manufacturing based on singular and combined toxicity assessments. This study showed the importance of considering combined toxicity for solvent selection.

Hyperbranched polymeric nanomaterials impair the freshwater crustacean Daphnia magna

Hyperbranched polymers are nanomaterials belonging to the class of dendritic architectures with increasing applications in many diverse fields. We studied the toxicity of two hyperbranched polymers to the freshwater crustacean Daphnia magna. A hyperbranched hydroxyl-terminated polyester and a commercial hyperbranched polyamidoamine, Helux-3316 were tested for the acute immobilization of daphnids, the overproduction of reactive oxygen species and the activity of the antioxidant enzymes catalase and glutathione S-transferase. The effect for D. magna immobilization was higher for the hyperbranched polyamidoamine Helux-3316, which was attributed to the presence of primary amino groups on its surface. Following exposure to both hyperbranched polymers, a clear overproduction of reactive oxygen species took place accompanied by concentration-dependent enzymatic antioxidant response. Our results showed that the overproduction of reactive oxygen species activated antioxidant defence mechanisms and was responsible for the immobilization of daphnids exposed to both hyperbranched polymers. We showed evidence of the uptake of fluorescently labelled Helux-3316 that accumulated into the gastrointestinal tract of D. magna, and its removal via excretion within fecal pellets. This is the first work reporting the internalization of hyperbranched polymers in aquatic organisms.

Short-term low salinity mitigates effects of oil and dispersant on juvenile eastern oysters: A laboratory experiment with implications for oil spill response activities

Following the Deepwater Horizon oil spill, eastern oyster (Crassostrea virginica) reefs in the northern Gulf of Mexico were exposed to oil and various associated clean-up activities that may have compromised oyster reef health. Included in the exposure was oil, dispersant, and in some locales, atypical salinity regimes. Oil and dispersants can be detrimental to oysters and the effects of salinity depend on the level. In addition to these extrinsic factors, genetic diversity of oyster populations may help the oysters respond to stressors, as demonstrated in other systems. We used a 3×3×2 factorial design to experimentally examine the effects of oil/dispersed oil, intraspecific genetic diversity, and salinity on juvenile (ca. 25 mm shell height) oyster survivorship and growth during a 21-d exposure in a closed, recirculating system. The genetic effect was weak overall, oil and dispersed oil negatively affected juvenile oyster survivorship, and low salinity mitigated mortality in oil and dispersed oil treatments. Survivorship was about 40% greater in low-salinity than in mesohaline water for both oil and dispersed oil treatments, bringing survivorship in low salinity oil-only treatments to a similar level with low salinity controls (no oil). Oyster growth was minimal after 21 d but appeared to be negatively affected by oil and dispersed oil, and had a significant interaction with salinity. Our results may be informative for future decisions regarding oil spill response activities and suggest that a pulse of low salinity water may be a viable short-term mitigation option for oysters if filtration characteristics, exposure time, and water temperatures are all considered, in addition to weighing the costs and benefits of this type of response on other organisms and habitats.