Acute toxicity of current and alternative oil spill chemical dispersants to early life stage blue crabs (Callinectes sapidus)

• We examined the acute toxicity of five chemical dispersants on blue crab zoea.
• Blue crab zoea were most sensitive to Dispersit SPC 1000.
• Swimming activity and larval mobility decreased with increasing dispersant dose.
• Immobility of larvae was reached in doses below LC50 values for all dispersants.

The aim of this study was to examine the acute toxicity of five oil spill chemical dispersants on the ecologically and economically important coastal and estuarine species, blue crab Callinectes sapidus. Static, non-renewal 48 h acute toxicity tests were performed on stage-II blue crab zoea. The median lethal concentration (LC50) was calculated for each dispersant at 24 h and 48 h using nominal concentrations for each dispersant tested. The 48 h LC50 values from the most to the least toxic ranged from 10.1 mg L−1 for Dispersit SPC 1000 to 76.5 mg L−1 for Orca. For all dispersants, the swimming activity and mobility of larvae decreased with increasing dispersant concentration within 24 h of exposure and reached relative immobility at concentrations below LC50 values. These results show that the dispersants examined in this study are only slightly toxic after 48 h exposure to the earliest life stage of blue crabs that might likely be exposed to dispersants in the environment, with the exception of Dispersit SPC 1000 that bordered between slightly and moderately toxic. Although the dispersants themselves appear to not cause substantial acute toxicity, sublethal and potentially delayed impacts, such as, reduced mobility or food source availability could indirectly remove larvae from the population and need to be further examined, as do larval responses in standard chronic toxicity tests. Furthermore, dispersants are not released into the environment in isolation and so the impact of dispersed-oil using these dispersant formulations also needs to be investigated to translate into real-world situations.