Summary

Description

Shortterm, static exposure toxicity tests were conducted in the New Jersey Field Office laboratory to evaluate the potential for the water accommodated fractions of Arab light crude oil which is transported in large quantities through Delaware Bay and Corexit.9527 the most commonly used dispersant in the United States to adversely affect gametes, fertilization and early postfertilization development of the horseshoe crab Limulus polyphemus. Gametes were obtained from adult horseshoe crabs using a modified Arbacia stimulator. This method yielded sufficient viable gametes for toxicity tests without harming the adults. Eggs and sperm were exposed to seawater or one of five concentrations four replicates concentration of oil, 1:10 dispersant:oil mix, or dispersant only. Toxicant solutions were prepared using methods described in the National Oil Spill Contingency Plan 40 CFR Parts 9 and 300. Measured concentrations of total petroleum hydrocarbons TPH in exposure water prepared with oil only ranged from 1.0 ppm to 4.8 ppm. In addition, concentrations of total polynuclear aromatic hydrocarbons PAHs ranged from 0.0002 to 0.045 ppm and the summed concentrations of the volatile monoaromatic hydrocarbons BTEX ranged from 0.01 to 0.18 ppm. In exposure water prepared with oil and dispersant, TPH concentrations ranged from 1.0 to 88 ppm, concentrations of total PAHs ranged from 0.0002 to 0.600 and summed concentrations of volatile compounds ranged from 0.01 to 0.74 ppm. Dispersant concentrations were not measured. Nominal dispersant concentrations ranged from 1.0 to 100 ppm. Maximum total PAH concentrations and all the nominal dispersant concentrations used in this study exceeded adverse effect levels reported for sensitive marine species. Toxicant exposure lasted 24 hours after which embryos were maintained in clean water. Chambers were checked at the beginning of exposure for evidence of sperm viability activation upon introduction to eggs and fertilization success granulation and percent viable embryos after 48 hours. After transfer to clean water, chambers were monitored for evidence of successful development to the blastula stage. At 25C, development proceeded to early stages of germ disc formation before observations were terminated. Exposure to dispersant resulted in activation of sperm even when eggs were not present. The threshold concentration of Corexit 9527 for this effect was between 10 and 50 ppm. In the field, the timing of egg and sperm release is such that activation stimulated by dispersant is not considered to be an adverse effect. Sperm were activated by the presence of eggs even during exposure to the most concentrated oil, dispersant and oil, or dispersant test solutions used. The fraction of eggs that was successfully fertilized during exposure to toxicant mixtures approximately 80 was not different from that observed in controls. The percentages of viable embryos observed after 48 hours were the same as percentages that reached the blastula stage of development approximately 96 hours, suggesting that 1 development to the blastula stage was not affected by initial exposure to toxicant mixtures, and 2 viability at 48 hours may be a reasonable index of the potential for successful development to later stages. It is concluded that gametes, fertilization and early embryonic development of the horseshoe crab were not adversely affected by exposure to water mixed with arab light crude oil, Arab light crude oil and Corexit 9527, or Corexit 9527 alone, even when total PAH and dispersant concentrations in some test mixtures exceeded levels that are toxic to sensitive marine species.