Developmental effects in fish embryos exposed to oil dispersions - The impact of crude oil micro-droplets.

During accidental crude oil spills and permitted discharges of produced water into the marine environment, a large fraction of naturally occurring oil components will be contained in micron-sized oil droplets. Toxicity is assumed to be associated with the dissolved fraction of oil components, however the potential contribution of oil droplets to toxicity is currently not well known. In the present work we wanted to evaluate the contribution of oil droplets to effects on normal development of Atlantic cod (Gadus morhua) through exposing embryos for 96 h to un-filtered (dispersions containing droplets) and filtered (water soluble fractions) dispersions in a flow-through system at dispersion concentrations ranging from 0.14 to 4.34 mg oil/L. After exposure, the embryos were kept in clean seawater until hatch when survival, development and morphology were assessed. The experiment was performed at two different stages of embryonic development to cover two potentially sensitive stages (gastrulation and organogenesis). Exposure of cod embryos to crude oil dispersions caused acute and delayed toxicity, including manifestation of morphological deformations in hatched larvae. Oil droplets appear to contribute to some of the observed effects including mortality, larvae condition (standard length, body surface, and yolk sac size), spinal deformations as well as alterations in craniofacial and jaw development. The timing of exposure may be essential for the development of effects as higher acute mortality was observed when embryos were exposed from the start of gastrulation (Experiment 1) than when exposed during organogenesis (Experiment 2). Even though low mortality was observed when exposed during organogenesis, concentration-dependent mortality was observed during recovery.

Reproduction dynamics in copepods following exposure to chemically and mechanically dispersed crude oil.

Conflicting reports on the contribution of chemical dispersants on crude oil dispersion toxicity have been published. This can partly be ascribed to the influence of dispersants on the physical properties of the oil in different experimental conditions. In the present study the potential contribution of dispersants to the reproductive effects of dispersed crude oil in the marine copepod Calanus finmarchicus (Gunnerus) was isolated by keeping the oil concentrations and oil droplet size distributions comparable between parallel chemically dispersed (CD, dispersant:oil ratio 1:25) and mechanically dispersed oil (MD, no dispersant) exposures. Female copepods were exposed for 96 h to CD or MD in oil concentration range of 0.2-5.5 mg·L(-1) (THC, C5-C36) after which they were subjected to a 25-day recovery period where production of eggs and nauplii were compared between treatments. The two highest concentrations, both in the upper range of dispersed oil concentrations reported during spills, caused a lower initial production of eggs/nauplii for both MD and CD exposures. However, copepods exposed to mechanically dispersed oil exhibited compensatory reproduction during the last 10 days of the recovery period, reaching control level of cumulative egg and nauplii production whereas females exposed to a mixture of oil and dispersant did not.