Effects of a Branched p-Nonylphenol Isomer (4(3 -,6 -dimethyl-3 -heptyl)-phenol) on Embryogenesis in Lymnae stagnalis L.

Abstract

The tertiary branched alkyl-chain isomers of p-nonylphenol (NP) are perceived to have more estrogenic potency than its constituent secondary and primary straight alkyl-chain isomers. Investigations with single tertiary branched isomers ofNP can therefore contribute toward the elucidation ofthe mechanisms oftoxicity and estrogenicity of NP. A single tertiary branched alkyl-chain isomer (4(3 -,6 - dimethyl-3 -heptyl)-phenol) was used in studies to determine its effects on embryonic growth and mortality in Lymnaea stagnalis L. Egg masses were exposed to the test compound for 20 days in a static waterborne-exposure regime with an average NP concentration of105 lg/L and water temperature range of18–20 C. Observations were made under a microscope and pictures were taken with a digital camera to determine the various developmental stages ofgrowth, the duration ofgrowth in each stage, embryo hatchability, and embryo mortality. The isomer was found to cause significant delay in all stages ofgrowth and more significantly in the Morula and Veliger stages. An increase in embryo mortality, from the third day until the end ofthe experiment, was observed in exposed egg masses compared to controls. The hatching success of embryos was also significantly reduced by exposure, with 81% hatchability in exposed egg masses compared to 93% in the controls, after 18 days of continuous exposure. The encapsulating jelly strand that completely covers the rows ofegg masses may have prevented the isomer residues from effectively penetrating into the embryos as shown by the observed low bioconcentration factors of the isomer in egg masses during exposure, resulting in unexpectedly lower observed estrogenic effects. However, this factor was not investigated. In vivo biotransformation ofsome ofthe residues of the isomer into catechol metabolites by the embryos during exposure could also result in the reduction ofits estrogenic potential. To understand more fully the extent of toxicity and estrogenicity ofthis isomer, in vitro estrogenic assays are recommended. It would also be necessary to investigate its estrogenic effects on embryo development after in vivo maternal exposure.