Matthew M. Alloy

Effects of Suspended Multi-Walled Carbon Nanotubes on Daphnid Growth and Reproduction

Relatively little is known about the potential impacts of engineered nanoparticles on aquatic biota. Particularly relevant to aquatic ecosystems are those particles, which display increased solubility either through specialized coatings or through an ability to interact with water column constituents such as natural organic matter (NOM). Previous research has indicated that grazing zooplankton (Daphnia magna) are able to ingest lipid-coated single-walled carbon nanotubes (SWNTs) from the water column during their normal feeding behavior (Roberts et al., 2007). Acute mortality was observed only at high concentrations (>5mg/L). In this research NOM was used in place of a surfactant to stabilize suspensions. Water chemistry (ionic strength, hardness, and pH) has been shown to alter the behavior of NOM in natural systems. We hypothesized that these same variables may also affect the toxicity of multi-walled carbon nanotubes (MWNT) stabilized in NOM. The purpose of this research was to examine the potential for sublethal effects to occur following exposure to multi-walled carbon nanotubes suspended in NOM and to determine whether those effects vary with pH alterations.

Photo-induced toxicity of titanium dioxide nanoparticles to Daphnia magna under natural sunlight

Titanium dioxide nanoparticles (TiO2 NP) are one of the most abundantly utilized nanoparticles in the world. Studies have demonstrated the ability of the anatase crystal of TiO2 NP to produce reactive oxygen species (ROS) in the presence of ultraviolet radiation (UVR), a co-exposure likely to occur in aquatic ecosystems. The goal of this study was to examine the photo-induced toxicity of anatase TiO2 NP under natural sunlight to Daphnia magna. D. magna were exposed to a range of UVR intensities and anatase TiO2 concentrations in an outdoor exposure system using the sun as the source of UVR. Different UVR intensities were achieved using UVR opaque and transparent plastics. AnataseTiO2-NP demonstrated the reciprocal relationship seen in other phototoxic compounds such as polycyclic aromatic hydrocarbons (PAHs) at higher UVR treatments. The calculated 8h LC50 of anatase TiO2 NP was 139 ppb under full intensity ambient natural sunlight, 778 ppb under 50% natural sunlight, and >500 ppm under 10% natural sunlight. Mortality was also compared between animals allowed to accumulate a body burden of anatase TiO2 for 1h and organisms whose first exposure to anatase TiO2 aqueous suspensions occurred under UVR. A significantly greater toxic effect was observed in aqueous, low body burden suspensions than that of TiO2 1h body burdens, which is dissimilar from the model presented in PAHs. Anatase TiO2 presents a unique photo-induced toxic model that is different than that of established phototoxic compounds.

Ultraviolet Radiation Enhances the Toxicity of Deepwater Horizon Oil to Mahi-mahi (Coryphaena hippurus) Embryos

The 2010 Deepwater Horizon oil spill resulted in the accidental release of millions barrels of crude oil into the Gulf of Mexico. Photoinduced toxicity following coexposure to ultraviolet (UV) radiation is one mechanism by which polycyclic aromatic hydrocarbons (PAHs) from oil spills may exert toxicity. Mahi-mahi (Coryphaena hippurus), an important fishery resource, have positively buoyant, transparent eggs. These characteristics may result in mahi-mahi embryos being at particular risk from photoinduced toxicity. The goal of this study was to determine whether exposure to ultraviolet radiation as natural sunlight enhances the toxicity of crude oil to embryonic mahi-mahi. Mahi-mahi embryos were exposed to several dilutions of water accommodated fractions (WAF) from slick oil collected during the 2010 spill and gradations of natural sunlight in a fully factorial design. Here, we report that coexposure to natural sunlight and WAF significantly reduced percent hatch in mahi-mahi embryos. Effect concentrations of PAH in WAF were within the range of surface PAH concentrations reported in the Gulf of Mexico during the Deepwater Horizon spill. These data suggest that laboratory toxicity tests that do not include UV may underestimate the toxicity of oil spills to early lifestage fish species.

Photo-induced toxicity of Deepwater Horizon slick oil to blue crab (Callinectes sapidus) larvae.

The 2010 Deepwater Horizon oil spill resulted in the accidental release of approximately 700 million L of crude oil into the Gulf of Mexico. Photo-induced toxicity after co-exposure to ultraviolet (UV) radiation is 1 mechanism by which polycyclic aromatic hydrocarbons (PAHs) from oil spills may exert toxicity. Blue crab are an important commercial and ecological resource in the Gulf of Mexico, and their largely transparent larvae may make them sensitive to PAH photo-induced toxicity. The goal of the present study was to examine the sensitivity of early lifestage blue crab (Callinectes sapidus) zoea to slick oil collected during the Deepwater Horizon spill. Blue crab zoea were exposed to 1 of several dilutions of water accommodated fractions from 1 of 2 sources of oil and gradations of natural sunlight in a factorial design. Two 7-h solar exposures were carried out with a recovery period (dark) in between. Survival was found to be UV- and PAH-dependent. Toxicity was observed within the range of surface PAH concentrations reported in the Gulf of Mexico during the Deepwater Horizon spill. These findings indicate that early lifestage blue crab are sensitive to photo-induced toxicity from Deepwater Horizon slick oil.

A novel system for embryo-larval toxicity testing of pelagic fish: Applications for impact assessment of Deepwater Horizon crude oil

Key differences in the developmental process of pelagic fish embryos, in comparison to embryos of standard test fish species, present challenges to obtaining sufficient control survival needed to successfully perform traditional toxicity testing bioassays. Many of these challenges relate to the change in buoyancy, from positive to negative, of pelagic fish embryos that occurs just prior to hatch. A novel exposure system, the pelagic embryo-larval exposure chamber (PELEC), has been developed to conduct successful bioassays on the early life stages (ELSs; embryos/larvae) of pelagic fish. Using this unique recirculating upwelling system, it was possible to significantly improve control survival in pelagic fish ELS bioassays compared to commonly used static exposure methods. Results demonstrate that control performance of mahi-mahi (Coryphaena hippurus) embryos in the PELEC system, measured as percent survival after 96-hrs, significantly outperformed agitated static exposure and static exposure systems. Similar significant improvements in 72-hr control survival were obtained with yellowfin tuna (Thunnus albacares). The PELEC system was subsequently used to test the effects of photo-induced toxicity of crude oil to mahi-mahi ELSs over the course of 96-hrs. Results indicate a greater than 9-fold increase in toxicity of Deepwater Horizon (DWH) crude oil during co-exposure to ambient sunlight compared to filtered ambient sunlight, revealing the importance of including natural sunlight in 96-hr DWH crude oil bioassays as well as the PELEC systems potential application in ecotoxicological assessments.

Exposure to ultraviolet radiation late in development increases the toxicity of oil to mahi‐mahi (Coryphaena hippurus) embryos

The Deepwater Horizon oil spill in 2010 overlapped with the spawning of many pelagic fish species in the Gulf of Mexico, including mahi-mahi (Coryphaena hippurus). Polycyclic aromatic hydrocarbons (PAHs) released during the spill have been shown to cause photo-induced toxicity under ultraviolet (UV) radiation. In the present study, mahi-mahi embryos were exposed to high-energy water accommodated fractions of source and naturally weathered oils for up to 48 h. The timing of co-exposure with UV radiation varied between an early development exposure for 8 h or a late development exposure for 8 h. The UV co-exposure had a photo-induced toxic effect on hatching success for all oil types and exposure scenarios. A more sensitive developmental window to photo-induced toxicity was observed when UV exposure occurred late in development. Source Oil B was over 6-fold more toxic, and Massachusetts source oil was 1.6-fold more toxic when the embryos were co-exposed to UV light late in development. Furthermore, weathered oil from the surface co-exposure with UV late in development resulted in bradycardia in the mahi-mahi. The present study provides evidence that the developmental window when UV co-exposure occurs has a significant effect on the degree of photo-induced toxicity of oil and that UV co-exposure may exacerbate long-term cardiac effects in developing fish. Environ Toxicol Chem 2017;36:1592-1598.

Co-exposure to sunlight enhances the toxicity of naturally weathered Deepwater Horizon oil to early lifestage red drum (Sciaenops ocellatus) and speckled seatrout (Cynoscion nebulosus)

The 2010 Deepwater Horizon oil spill resulted in the accidental release of millions of barrels of crude oil into the Gulf of Mexico. Photo-induced toxicity following co-exposure to ultraviolet (UV) radiation is 1 mechanism by which polycyclic aromatic hydrocarbons (PAHs) from oil spills may exert toxicity. Red drum and speckled seatrout are both important fishery resources in the Gulf of Mexico. They spawn near-shore and produce positively buoyant embryos that hatch into larvae in approximately 24 h. The goal of the present study was to determine whether exposure to UV as natural sunlight enhances the toxicity of crude oil to early lifestage red drum and speckled seatrout. Larval fish were exposed to several dilutions of high-energy water-accommodated fractions (HEWAFs) from 2 different oils collected in the field under chain of custody during the 2010 spill and 3 gradations of natural sunlight in a factorial design. Co-exposure to natural sunlight and oil significantly reduced larval survival compared with exposure to oil alone. Although both species were sensitive at PAH concentrations reported during the Deepwater Horizon spill, speckled seatrout demonstrated a greater sensitivity to photo-induced toxicity than red drum. These data demonstrate that even advanced weathering of slicks does not ameliorate the potential for photo-induced toxicity of oil to these species. Environ Toxicol Chem 2017;36:780-785.

Effect of natural organic matter on the photo‐induced toxicity of titanium dioxide nanoparticles

Nano-titanium dioxide (TiO2 ) is the most widely used form of nanoparticles in commercial industry and comes in 2 main configurations: rutile and anatase. Rutile TiO2 is used in ultraviolet (UV) screening applications, whereas anatase TiO2 crystals have a surface defect that makes them photoreactive. There are numerous reports in the literature of photo-induced toxicity to aquatic organisms following coexposure to anatase nano-TiO2 and UV. All natural freshwater contains varying amounts of natural organic matter (NOM), which can drive UV attenuation and quench reactive oxygen species (ROS) in aquatic ecosystems. The present research examined how NOM alters the photo-induced toxicity of anatase nano-TiO2 . Daphnia magna neonates were coexposed to NOM and photoexcited anatase nano-TiO2 for 48 h. Natural organic matter concentrations as low as 4 mg/L reduced anatase nano-TiO2 toxicity by nearly 100%. These concentrations of NOM attenuated UV by <10% in the exposure system. However, ROS production measured using a fluorescence assay was significantly reduced in a NOM concentration--dependent manner. Taken together, these data suggest that NOM reduces anatase nano-TiO2 toxicity via an ROS quenching mechanism and not by attenuation of UV. Environ Toxicol Chem 2017;36:1661-1666.

Photo-induced toxicity in early life stage fiddler crab (Uca longisignalis) following exposure to Deepwater Horizon oil

The 2010 explosion of the Deepwater Horizon (DWH) oil rig led to the release of millions of barrels of oil in the Gulf of Mexico. Oil in aquatic ecosystems exerts toxicity through multiple mechanisms, including photo-induced toxicity following co-exposure with UV radiation. The timing and location of the spill coincided with both fiddler crab reproduction and peak yearly UV intensities, putting early life stage fiddler crabs at risk of injury due to photo-induced toxicity. The present study assessed sensitivity of fiddler crab larvae to photo-induced toxicity during co-exposure to a range of environmentally relevant dilutions of high-energy water accommodated fractions of DWH oil, and either <10, 50, or 100% ambient sunlight, achieved with filters that allowed for variable UV penetration. Solar exposures (duration: 7-h per day) were conducted for two consecutive days, with a dark recovery period (duration: 17-h) in between. Survival was significantly decreased in treatments the presence of >10% UV and relatively low concentrations of oil. Results of the present study indicate fiddler crab larvae are sensitive to photo-induced toxicity in the presence of DWH oil. These results are of concern, as fiddler crabs play an important role as ecosystem engineers, modulating sediment biogeochemical processes via burrowing action. Furthermore, they occupy an important place in the food web in the Gulf of Mexico.

Estimating incident ultraviolet radiation exposure in the northern Gulf of Mexico during the Deepwater Horizon oil spill

Millions of barrels of oil were released into the Gulf of Mexico following the 2010 explosion of the Deepwater Horizon oil rig. Polycyclic aromatic hydrocarbons (PAHs) are toxic components of crude oil, which may become more toxic in the presence of ultraviolet (UV) radiation, a phenomenon known as photo-induced toxicity. The Deepwater Horizon spill impacted offshore and estuarine sites, where biota may be co-exposed to UV and PAHs. Penetration of UV into the water column is affected by site-specific factors. Therefore, measurements and/or estimations of UV are necessary when one is assessing the risk to biota posed by photo-induced toxicity. We describe how estimates of incident UV were determined for the area impacted by the Deepwater Horizon oil spill, using monitoring data from radiometers near the spill, in conjunction with reference spectra characterizing the composition of solar radiation. Furthermore, we provide UV attenuation coefficients for both near- and offshore sites in the Gulf of Mexico. These estimates are specific to the time and location of the spill, and fall within the range of intensities utilized during photo-induced toxicity tests performed in support of the Deepwater Horizon Natural Resource Damage Assessment (NRDA). These data further validate the methodologies and findings of phototoxicity tests included in the Deepwater Horizon NRDA, while underscoring the importance of considering UV exposure when assessing possible risks following oil spills. Environ Toxicol Chem 2018;37:1679-1687.