Effects of Photosystem II inhibiting herbicides on mangroves—preliminary toxicology trials Alicia M. Bell, Norman C. Duke * Centre for Marine Studies, The University of Queensland, St Lucia, Queensland 4072, Australia Abstract Mangroves are sensitive to the root application of Photosystem II inhibiting herbicides and Avicennia marina is more sensitive thanothermangrovestested.Seedlingsoffourmangrovespecies,includingtwosalt-excretingspecies(A. marina and Aegiceras corn- iculatum)andtwosalt-excludingspecies(Rhizophora stylosa and Ceriops australis)weretreatedwitharangeofconcentrationsofthe herbicides diuron, ametryn and atrazine. Assessment of responses required the separation of seedlings into two groups: those that hadonlytheirrootsexposedtotheherbicidesthroughthewater(A. marina and R. stylosa)andthosethathadbothrootsandleaves exposed to herbicides through the water (A. corniculatum and C. australis). Salt-excreting species in each group were more suscep- tibletoallherbicidetreatmentsthansalt-excludingspecies,indicatingthatrootphysiologywasamajorfactorintheuptakeoftoxic pollutants in mangroves. Submergence of leaves appeared to facilitate herbicide uptake, having serious implications for seedling recruitmentinthefield.Eachherbicidewasrankedbyitstoxicitytomangroveseedlingsfrommostdamagingtoleasteffective,with diuron > ametryn > atrazine. The relative sensitivity of A. marina found in these pot trials was consistent with the observed sensi- tivityofthisspeciesinthefield,notablywhereseverediebackhadspecificallyaffected A. marina intheMackayregion,northeastern Australia. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Mangrove; Avicennia marina; Herbicide; Diuron; Impact; Australia 1. Introduction Duetotherapidgrowthofhumanpopulationsalong coastlines and adjacent estuarine areas, mangroves and their surrounding ecosystems are likely to be subjected to increasing amounts of land-derived contaminants via urban stormwater, effluent discharges and agricul- tural runoff (Giuffre de Lopez Camelo et al., 1997; Peters et al., 1997; Cavanagh et al., 1999; Haynes and Johnson, 2000; Zheng et al., 2000). Mangrove ecosys- temswerereportedlyresistanttoanumberofanthropo- genic inputs, including sewage outflow (Wong et al., 1995; Tam and Wong, 1999) and heavy metal pollution (Walsh et al., 1979; Chiu and Chou, 1991). However, therehasbeennoevidencereportedoftheeffectsofher- bicide pollution from runoff. Trace levels of herbicides havebeenfrequentlydetectedingroundwater(Baskaran et al., 2002),ponds(Kreuger et al., 1999), rivers, estuar- ies and oceans (Cavanagh et al., 1999; Haynes et al., 2000; Johnson and Ebert, 2000). More recently, wide- spread dieback of one mangrove species, Avicennia marina, was reported from the Mackay region of Queensland, north-eastern Australia (Duke et al., 2003).Thisunusualformofdiebackwasassociatedwith contamination by herbicides, particularly of diuron, washed down in runoff from agricultural lands (Duke and Bell, in press). Dieback was observed in at least five adjacent estuaries in the region. In this case, Avicennia marina was specifically affected by this dieback, of approximately 20 mangrove species in the area. 0025-326X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2004.10.051 * Corresponding author. Tel.: +61 7 3365 2729; fax: +61 7 3365 7321. E-mail address: n.duke@uq.edu.au (N.C. Duke). www.elsevier.com/locate/marpolbul Marine Pollution Bulletin 51 (2005) 297–307