Myrrh-derived terpenoids as inhibitors of marine biofouling

Abstract

With the recent ban on organotin-containing antifouling coatings by the International Maritime Organisation and doubts about paints containing copper, there is a pressing need for environmentally benign antifoulants. In the current study, we investigated the use of opoponax essential oil (scented myrrh Commiphora guidotti), its constituent terpenes/oids: ocimene, β-bisabolene, α-bisabolol and farnesol, and sandalwood essential oil in this role. Assays using cypris larvae of the barnacle Balanus amphitrite revealed that coatings of the sesquiterpenoid alcohols (farnesol and α-bisabolol) and sandalwood essential oil (determined by a gas chromatograph-flame ionisation detector to consist of 78.1% santolol, another sesquiterpenoid alcohol) were the most larvicidal. The LC50 values after 48 h were 18 (farnesol), 88 (α-bisabolol) and 165 μg well-1 (sandalwood essential oil). No anti-settlement was observed without accompanying larvicidal activity and no synergistic effects were seen when oils were used in combination. Farnesol and α-bisabolol exhibited very low leaching rates into assay water, suggesting that cyprid mortality may have resulted from direct contact with the coatings. Extending the duration of these assays from 48 to 120 h increased settlement in controls but did not reveal additional anti-settlement activity in the presence of oils. Inclusion of the settlement inducer, 3-isobutyl-1-methylxanthine (IBMX, 10-5 M) increased settlement in controls and demonstrated anti-settlement activity in opoponax essential oil without any significant cyprid mortality. Field trials that incorporated opoponax essential oil or the terpenes/oids into marine paint either individually or in 1:1 mixtures did not show clear evidence of antifouling activity at the concentrations tested. © Inter-Research 2008.