The acute toxicity of chemically and physically dispersed crude oil to key arctic species under arctic conditions during the open water season

Abstract

The acute toxicity of physically and chemically dispersed crude oil and the dispersant Corexit 9500 were evaluated for key Arctic species. The copepod Calanus glacialis, juvenile Arctic cod (Boreogadus saida), and larval sculpin (Myoxocephalus sp.) were tested under conditions representative of the Beaufort and Chukchi Seas during the ice-free season. The toxicity of 3 water-accommodated fractions (WAF) of Alaska North Slope crude oil was examined with spiked, declining exposures. A dispersant-only test was conducted with the copepod C. glacialis. Each preparation with oil (WAF, breaking wave WAF [BWWAF], and chemically enhanced WAF [CEWAF]) produced distinct suites of hydrocarbon constituents; the total concentrations of oil were lowest in WAF and highest in CEWAF preparations. The relative sensitivity for the different species and age classes was similar within each WAF type. Median lethal concentration values based on total petroleum hydrocarbons ranged from 1.6 mg/L to 4.0 mg/L for WAF and BWWAF treatments and from 22 mg/L to 62 mg/L for CEWAF. For Corexit 9500 exposures, median lethal concentration values ranged from 17 mg/L to 50 mg/L. The differences in the relative toxicity among the accommodated fractions indicated that the majority of petroleum hydrocarbons in the CEWAF are in less acutely toxic forms than the components that dominate the WAF or BWWAF. Further evaluation showed that the parent polycyclic aromatic hydrocarbon compounds, specifically naphthalene, were highly correlated to acute toxicity. Environ Toxicol Chem 2013;32:2284–2300.

Some Thoughts on Estimating Change to Arctic Cod Populations from Hypothetical Oil Spills in the Eastern Alaska Beaufort Sea

“…We modeled two scenarios: physically dispersed oil and 100% chemically dispersed oil using COREXIT® 9500. Gardiner et al (2013) measured LC 50 values of 80 ppb PAH (polynuclear aromatic hydrocarbons) when Arctic cod juveniles were subjected to physically dispersed oil alone and 1640 ppb PAH when subjected to oil plus dispersant (chemically dispersed oil). These were the LC 50 values for the breaking wave water accommodated fraction (BW-WAF) and the chemically enhanced water accommodated fraction (CE-WAF) described by Gardiner et al (2013).…”

“…The panel concluded that data on the relative toxicity of crude oil and dispersed oil to pelagic and epipelagic organisms in the Arctic were limited and that additional toxicity data based on Arctic organisms tested under Arctic conditions were needed. This led to a toxicity research program as reported by Gardiner et al (2013). The acute toxicity of physically and chemically dispersed crude oil was evaluated for three Arctic species: the copepod Calanus glacialis, juvenile Arctic cod (Boreogadus saida), and larval sculpin (Myoxocephalus sp.).…”

“…The next step was to define oil spill scenarios describing the location of the spills, the meteorologic and oceanographic (metocean) conditions, the type of oil spilled, and the application of dispersants. Oil spill models were then used to determine the volume of water having oil constituent concentrations at or exceeding the 96 h acute toxicity thresholds (concentrations lethal to 50% of the organisms, called LC 50 ) determined by Gardiner et al (2013). All larval Arctic cod that occurred within this volume of water were assumed to be lost to the system.…”

“…The toxicity data for this study were provided by Gardiner et al (2013) and the larval and early juvenile stage density data were obtained from bongo net surveys of the Alaska Beaufort Sea shelf conducted in August-September of 2011 (Norcross et al 2017). Arctic cod collected in these surveys were measured and aged in days based on otolith microstructure.…”

An Experimental System to Assess Potential Biological Impact of Operational Response During an Oil Spill

“…For this reason, in an emergency context such an oil spill, it is necessary to have as soon as possible toxicity data to evaluate the potential biological impact. Many studies have evaluated the acute toxicity of dispersant alone [3][4][5][6] or dispersant enhanced water accommodated fractions [7][8][9][10]. These methods presented a major disadvantage.…”