Degradation and transformation of all-

Abstract

Environmental context Excessive amounts of retinoic acids (RAs), the main derivatives of vitamin A, cause developmental abnormalities in animals, yet information on their fate in the marine environment is limited. This study investigated the degradation of all-trans-RA in seawater and found that over 90% was degraded and transformed in unfiltered natural seawater within 24 h. The results provide essential insights on the fate and risks of RAs in marine environments. Rationale Retinoic acids (RAs) are crucial to the development of various animals. However, exposure to excessive concentrations of RAs can lead to teratogenic effects in aquatic species during their developmental stages. Some urbanised coastal marine environments receive a large amount of partially treated wastewater effluent and occasionally suffer from algal bloom incidents, both of which are considered important sources of RAs in the marine environment. Yet information on degradation and transformation of RAs in seawater is currently unavailable for assessment of their environmental risk. This study, therefore, aimed to investigate the degradation and transformation of all-trans-RA (at-RA), which is the most abundant and widely distributed RA in the marine environment. Methodology A laboratory experiment was conducted to examine the degradation and transformation of at-RA in six different types of seawater (i.e. artificial seawater, unfiltered and filtered natural seawater, each with or without autoclave treatment). Degradation and transformation products of at-RA were analysed using high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Results The experiment showed that at-RA could be instantly degraded and transformed into other isomers such as 9-cis-RA and 13-cis-RA when entering seawater. Over 80% of at-RA was degraded in the first 48 h regardless of the type of seawater. Discussion The presence of microorganisms and suspended organic matters could jointly facilitate the degradation and removal of at-RA from the water column. Further investigation is encouraged to reveal the influence of other factors (e.g. temperature, solar radiation, aeration) on the transformation and degradation of at-RA in seawater.