Comparative environmental safety and mechanism of toxicity of representative antifouling agents : SeaNine 211, butenolide, and 3,3'-diindolylmethane (DIM)

Abstract

A good antifouling compound not only needs to be efficacious against the settlement of fouling organisms, but also is required to be environmentally friendly. Because of the high toxicity and pollution in marine environment, the antifouling booster biocides currently in use are not the optimum solutions to biofouling problem. It is recognized that natural products isolated from living organisms will provide a plentiful resource for the development of environmentally friendly antifoulants. Therefore, in order to compare the relative applicability of antifouling booster biocides and natural products, this thesis work employed three representative antifoulants, SeaNine 211 of booster biocide together with butenolide and 3,3'-diindolylmethane (DIM) of natural product, and investigated their comparative degradation kinetics in marine environment and chronic toxicity using marine medaka (Oryzias melastigma), an increasingly-used model for marine toxicology. The results showed that butenolide could be degraded rapidly in natural seawater with half-life at 13.0 h while 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT), the active ingredient of SeaNine 211, and DIM had no obvious degradation after 96-h incubation. Furthermore, no toxic byproducts would be generated by the degradation of butenolide, as inferred from the decreasing toxicity along with degradation. Bacterial effects should be the major contributor to the biodegradation of butenolide. In addition, the degradation kinetics of antifoulants were found to depend on temperature heavily, indicating the seasonal variation of the applicability of antifouling agents. Chronic exposure of adult medaka to antifouling compounds revealed that butenolide was relatively safer compared with DCOIT and DIM in terms of oxidative stress, neurotoxicity, endocrine disruption and reproductive impairment. Proteomic profiling indicated that the activated detoxification system in liver may account for the biosafety of butenolide. DCOIT was determined to be a moderate disruptor of endocrine homeostasis. It showed estrogenic activity mainly in male fish at environmentally realistic concentrations. Transgenerational toxicity of DCOIT was also reflected on the decreased viability of medaka larvae, such as delayed hatching and lethargic swimming. Compared with butenolide and DCOIT, DIM was very potent on endocrine disruption. It behaved estrogenic in males but anti-estrogenic in females along with the hypothalamus-pituitary-gonadal-liver (HPGL) axis. There were significantly decreased levels of vitellogenin (VTG) and choriogenin, proteins for the yolk and egg envelop of medaka eggs, in females but increased levels in males. The deficiency in VTG and choriogenin speculatively resulted in the decreased fecundity and impaired viability of offspring. Genomic profiling of gonads at the transcript and protein levels further identified a series of biochemical processes that plotted an Adverse Outcome Pathway (AOP) from bottom up, which linked the molecular initiating events with the apical adverse outcomes including egg production and swimming behavior. In summary, after taking the degradation, toxicity and activity into combined consideration, we can generally conclude that butenolide is a promising antifouling compound in view of its fast degradation, biosafety and efficacious antifouling activity. More work are thus warranted to obtain a clear understanding of the properties of butenolide to facilitate its future registration and commercialization. For DCOIT, it is arguing for systematic investigation of its ecological risks in certain area because it can not be degraded rapidly in the waters of Hong Kong and shows endocrine disruptive effects. However, with regard to the chemical stability and strong toxicity on endocrine homeostasis and reproductive performance, DIM is not suitable for antifouling usage.

Date of Award	2016
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology