Carbon Nanotube Properties Influence Adsorption of Phenanthrene and Subsequent Bioavailability and Toxicity to Pseudokirchneriella subcapitata

The bioavailability of organic contaminants adsorbed to carbon nanotubes (CNTs) remains unclear, especially in complex natural freshwaters containing natural organic matter (NOM). Here, we report on the adsorption capacity (<i>Q</i>⁰) of five CNTs exhibiting different physicochemical properties, including a single-walled CNT (SWCNTs), multiwalled CNTs (MWCNT-15 and MWCNT-30), and functionalized MWCNTs (hydroxyl, −OH, and carboxyl, −COOH), for the model polycyclic aromatic hydrocarbon phenanthrene (3.1–800 μg/L). The influence of phenanthrene adsorption by the CNTs on bioavailability and toxicity was investigated using the freshwater algae Pseudokirchneriella subcapitata. CNTs were dispersed in algal growth media containing NOM (DOC, 8.77 mg/L; dispersed concentrations: 0.5, 1.3, 1.3, 3.3, and 6.1 mg/L for SWCNT, MWCNT-15, MWCNT-30, MWCNT–OH, and MWCNT–COOH, respectively). Adsorption isotherms of phenanthrene to the dispersed CNTs were fitted with the Dubinin–Ashtakhov model. Q⁰ differed among the CNTs, increasing with increasing surface area and decreasing with surface functionalization. SWCNT and MWCNT–COOH exhibited the highest and lowest log Q⁰ (8.891 and 7.636 μg/kg, respectively). The presence of SWCNTs reduced phenanthrene toxicity to algae (EC₅₀; 528.4) compared to phenanthrene-only (EC₅₀; 438.3), and the presence of MWCNTs had no significant effect on phenanthrene toxicity. However, phenanthrene adsorbed to NOM-dispersed CNTs proved to be bioavailable and contribute to exert toxicity to P. subcapitata

A simple protocol for estimating the acute toxicity of unresolved polar compounds from field-weathered oils

Crude oil spilled at sea is chemically altered through environmental processes such as dissolution, biodegradation, and photodegradation. Transformation of hydrocarbons to oxygenated species increases water-solubility. Metabolites and oxidation products largely remain uncharacterized by common analytical methods but may be more bioavailable to aquatic organisms. Studies have shown that unresolved (i.e. unidentified) polar compounds (‘UPCs’) may constitute > 90% of the water-accommodated fraction (WAF) of heavily weathered crude oils, but still there is a paucity of information characterizing their toxicological significance in relation to other oil-derived toxicants. In this study, low-energy WAFs (no droplets) were generated from two field-weathered oils (collected during the 2010 Deepwater Horizon incident) and their polar fractions were isolated through fractionation. To allow establishment of thresholds for acute toxicity (LC50) of the dissolved and polar fraction of field collected oils, we concentrated both WAFs and polar fractions to beyond field-documented concentrations, and the acute toxicity of both to the marine copepod Acartia tonsa was measured and compared to the toxicity of the native WAF (non-concentrated). The difference in toxic units (TUs) between the total of the mixture and of identified compounds of known toxicity (polycyclic aromatic hydrocarbons [PAHs] and alkyl phenols) in both WAF and polar fractions was used to estimate the contribution of the UPC to overall toxicity. This approach identified that UPC had a similar contribution to toxicity as identified compounds within the WAFs of the field-weathered oils. This signifies the relative importance of polar compounds when assessing environmental impacts of spilled and weathered oil.</p

Relative body burden (%) of select 2–6 ring PAHs and alkyl PAHs in larvae of cod exposed to ~9 μg/L tPAH, haddock exposed to WSF and haddock exposed to ~9 μg/L tPAH who hatched in the tank and that was dechorionated.

<p>NAP = naphthalene, FLU = fluorene, DBT = dibenzothiophene, PYR = pyrene, CHR = chrysene.</p

Coefficient of determination (R2) as a function of log KOW for the fit of a linear relationship between cyp1a induction and single compound body burdens.

<p>Coefficient of determination (R2) as a function of log KOW for the fit of a linear relationship between cyp1a induction and single compound body burdens.</p

Relative body burden (%) of select 2–6 ring PAHs and alkyl PAHs in larvae of cod exposed to ~9 μg/L tPAH, haddock exposed to WSF and haddock exposed to ~9 μg/L tPAH who hatched in the tank and that was dechorionated.

<p>NAP = naphthalene, FLU = fluorene, DBT = dibenzothiophene, PYR = pyrene, CHR = chrysene.</p

Deviation in body burden (pg/embryo) of PAHs and alkyl PAH groups between day 9 and day 3 for an intermediate exposure concentration (~3 μg/L tPAH).

<p>Negative values indicate a decline in body burden of the compound group between the two time points. NAP = naphthalene, FLU = fluorene, DBT = dibenzothiophene, PYR = pyrene, CHR = chrysene.</p

Observed relationship between log <i>K</i>_OW and rate of decline in body burden concentration from day 3 to day 9 during exposure of crude oil exposed haddock embryos.

<p>The fitted line shows a third-degree polynomial fit for 3–6 ring compounds (blue circles). 2-ring PAHs (red circles) showed a linear increase with increasing log <i>K</i>_OW.</p

Total PAH body burden (including alkyl clusters) measured in cod and haddock eggs at day 3 and day 9 of exposure.

<p>Total PAH body burden (including alkyl clusters) measured in cod and haddock eggs at day 3 and day 9 of exposure.</p

DataSheet1_Ingestion of car tire crumb rubber and uptake of associated chemicals by lumpfish (Cyclopterus lumpus).docx

Car tire rubber constitutes one of the largest fractions of microplastics emissions to the environment. The two main emission sources are tire wear particles (TWPs) formed through abrasion during driving and runoff of crumb rubber (CR) granulate produced from end-of-life tires that is used as infill on artificial sports fields. Both tire wear particles and crumb rubber contain a complex mixture of metal and organic chemical additives, and exposure to both the particulate forms and their leachates can cause adverse effects in aquatic species. An understanding of the exposure pathways and mechanisms of toxicity are, however, scarce. While the most abundant metals and organic chemicals in car tire rubber have multiple other applications, para-phenylenediamines (PDs) are primarily used as rubber antioxidants and were recently shown to cause negative effects in aquatic organisms. The present study investigated the responses of the marine lumpfish (Cyclopterus lumpus) to crumb rubber exposure in a controlled feeding experiment. Juvenile fish were offered crumb rubber particles with their feed for 1 week, followed by 2 weeks of depuration. Crumb rubber particle ingestion occurred in >75% of exposed individuals, with a maximum of 84 particles observed in one specimen. Gastrointestinal tract retention times varied, with some organisms having no crumb rubber particles and others still containing up to 33 crumb rubber particles at the end of the experiment. Blood samples were analyzed for metals and organic chemicals, with ICP-MS analysis revealing there was no uptake of metals by the exposed fish. Interestingly, high resolution GC-MS analysis indicated that uptake of PDs into lumpfish blood was proportionate to the number of ingested CR particles. Three of the PDs found in blood were the same as those identified in the additive mixture Vulkanox3100. N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) was the most concentrated PD in both the crumb rubber and lumpfish blood. The transformation product 6PPD-quinone was detected in the rubber material, but not in the blood. This study demonstrates that PDs are specific and bioavailable chemicals in car tire rubber that have the potential to serve as biomarkers of recent exposure to tire chemicals, where simple blood samples could be used to assess recent tire chemical exposure in vertebrates, including humans.</p

Comprehensive Two-Dimensional Gas Chromatography with Peak Tracking for Screening of Constituent Biodegradation in Petroleum UVCB Substances

Petroleum substances, as archetypical UVCBs (substances of unknown or variable composition, complex reaction products, or biological substances), pose a challenge for chemical risk assessment as they contain hundreds to thousands of individual constituents. It is particularly challenging to determine the biodegradability of petroleum substances since each constituent behaves differently. Testing the whole substance provides an average biodegradation, but it would be effectively impossible to obtain all constituents and test them individually. To overcome this challenge, comprehensive two-dimensional gas chromatography (GC × GC) in combination with advanced data-handling algorithms was applied to track and calculate degradation half-times (DT50s) of individual constituents in two dispersed middle distillate gas oils in seawater. By tracking >1000 peaks (representing ∼53–54% of the total mass across the entire chromatographic area), known biodegradation patterns of oil constituents were confirmed and extended to include many hundreds not currently investigated by traditional one-dimensional GC methods. Approximately 95% of the total tracked peak mass biodegraded after 64 days. By tracking the microbial community evolution, a correlation between the presence of functional microbial communities and the observed progression of DT50s between chemical classes was demonstrated. This approach could be used to screen the persistence of GC × GC-amenable constituents of petroleum substance UVCBs