Toxicity of sea-surface microlayer: Effects of hexane extract on baltic herring (Clupea harengus) and atlantic cod (Gadus morhua) embryos

Abstract This study was designed to determine whether contaminated sea-surface microlayer was toxic to marine fish embryos in its ntaive form and as a hexane extract. Developing embryos of Atlantic cod ( Gadus morhua ) and Baltic herring ( Clupea harengus ) were exposed to hexane extracts of sea-surface microlayer collected from five locations in the North Sea and Baltic Sea. Extracts from two of these locations produced significant embryos mortality as well as severe deformities in live hatched larvae. A control sample of bulk water collected from 20 cm under the surface and extracted in the same way produced no significant mortality or deformities. Significaant changes in timing of hatching were also observed in those samples which produced embryo toxic effects. A comparison of these data with those obtained from code embryos exposed to unextracted microlayer showed a similar biological effect with both unextracted samples and hexane extracts. Chemical analyses revealed the greatest biological effect in samples with petroleum hydrocarbon concentrations between 180 and > 200 μ g liter −1 . The bulk water control had 1 μg liter −1 while the three samples that showed no biological activity had 3 to 8 μg liter −1 petroleum hydrocarbons. Phthalic acid esters were detected in four samples and chlorinated hydrocarbons in one, but could not be positively correlated with any of the toxic responses. No other chemical contaminants were detected in the five samples. The data presented here show that some sites contain sea-surface microlayer which can be toxic to marine fish embryos: that Baltic herring and Atlantic cod embryos respond similarly to the toxic effects of contaminated microlayer: and that unextracted microlayer and hexane extract of microlayer produce essentially the same toxic effect(s) if only organic contaminants are considered.