Effects of pesticides on seagrass beds

Abstract

In the German Wadden Sea there has been a remarkable decline in seagrass beds. It was the aim of this study to test whether herbicide contamination could be a reason for this. Concentrations of triazine herbicides such as atrazine, simazine and terbutylazine as well as phenylurea herbicides were measured in Wadden Sea sediments within or in the neighbourhood of seagrass meadows. Sediments were thus used as a marker for medium-term contamination of the Wadden Sea. The respective concentrations were examined in relation to the density and status of the seagrass meadows. Preliminary results show that there may be a connection between seagrass decline and herbicide contamination in the parts of the Wadden Sea sampled. A comparison with other contamination is also given.Key words Wadden Sea · Seagrass beds · Herbicides · Zostera noltii · Sediments IntroductionSeveral millions of tons of pesticides are applied to fields annually world-wide (Bucheli et al. 1997;Müller et al. 1997) while about 30,000 t is used in each Germany and the Netherlands (Statistisches Bundesamt 1990;de Jong et al. 1995). Among these, herbicides are the most prominent followed by fungicides, while insecticides are less likely to be used in central and northern Europe, due to climatic conditions. It is estimated that about 1% of the pesticides applied reach the sea via rivers and the atmosphere (Bester 1996;Müller et al. 1997).About 600-800 t of pesticides thus reach the Wadden Sea annually. Some of these pesticides may have an effect on the marine ecosystems as has been shown in the case of atrazine affecting phytoplankton (Bester et al. 1995).Modern pesticides have different characteristics from the traditional ones such as like DDT and HCH. They have a low pK ow (2-4) and thus show little tendency to bioaccumulation. They are comparatively hydrophilic and polar and bind to sediment, which can be clay as well as organic material, via hydrogen bonds. Herbicides like the triazine pesticides (see Fig. 1) inhibit photosystem II, and by this mechanism they are able to have effects on all plants such as phytoplankton or possibly seagrass (Zostera noltii). These compounds can also be transformed to carcinogenic N-nitroso-derivatives. Little is known about the effects of the respective metabolites that have also been detected in the environment. In a political context it is interesting to note that though some derivatives (e.g. simazine and atrazine) are banned in Germany, there are dozens of derivatives of triazines and phenylureas (see Fig. 2) that are legally used in the EU.As the seagrasses have been diminished in the past (since 1970; see Kastler and Michaelis 1999) several reasons for this change have been discussed. While in some

Florida seagrass habitat evaluation: A comparative survey for chemical quality

“…The contribution of toxic chemicals to seagrass declines, the focus of this study, is largely unknown and has been investigated less frequently than the effects attributable to nutrient enrichment which is considered the primary cause of seagrass declines. However, some consider the impact of anthropogenic chemicals to be significant and worthy of increased investigation (Catsiki and Panayotidis, 1993;Short and Wyllie-Echeverria, 1996;Peters et al, 1997;SchlacherHoenlinger and Schlacher, 1998;Bester, 2000;Ralph, 2000).…”

Acute and additive toxicity of ten photosystem-II herbicides to seagrass

“…While there may be sufficient ecotoxicological data to derive guidelines for some PSII herbicides such as, atrazine, ametryn, diuron, hexazinone and tebuthiuron 18 , little is known of the relative toxicity of other PSII herbicides, such as bromacil, prometryn, metribuzin and fluometuron, which have also been detected in the GBR or its catchments 32 33 34 35 36 . Understanding the relative toxicities of these alternative PSII herbicides to tropical marine species, such as seagrass, is important for the sustainability and management of agricultural practices adjacent to the GBR catchment area and other locations where PSII herbicides are detected 27 37 38 39 .…”

Nonnutrient anthropogenic chemicals in seagrass ecosystems: Fate and effects

“…This is not surprising since the effects of excessive nutrients are considered by many to be the dominant anthropogenic cause of seagrass declines, particularly in urbanized coastal areas [13] where eutrophication is a common problem [22]. Nevertheless, it is thought that potentially phytotoxic, nonnutrient chemicals may also be a contributing factor to seagrass losses and deserving of increased scrutiny (examples [23][24][25][26]). Seagrasses are susceptible to the adverse effects of anthropogenic chemicals ( Fig.…”