Abstract
Efforts to develop generally applicable criteria or standards for environmental quality for the purpose of protecting South Africa’s rich biodiversity are normally hampered by the fact that species can differ considerably in their sensitivity to toxic substances. Direct extrapolation from one species to another is therefore not possible. By actually using this variation in sensitivity of species, the assessment of risk posed by contaminants may be placed on a more rigorous scientific footing. This concept holds that if quality criteria are accepted which would protect the most sensitive species, all other species are automatically protected. This article focuses on the use of sensitivity distributions of species as method and critically reviews the nature and applications of extrapolation models which are based on these distributions. Their possible use and arguments for and against such use are discussed. The conclusion is drawn that species sensitivity distributions have useful applications but data on the sensitivities of local species are scarce. Although already useful, this methodology can find more general application in South Africa if more research is undertaken to obtain reliable toxicity data for different species. In order to do that standardized toxicity tests for local species will have to be developed.
Highlights
Efforts to develop generally applicable criteria or standards for environmental quality for the purpose of protecting South Africa’s rich biodiversity are normally hampered by the fact that species can differ considerably in their sensitivity to toxic substances
Die volhoubare bewaring en beskerming van hierdie biologiese diversiteit is deel van die Verenigde Volke se Rio Konvensie wat in 1992 deur Suid-Afrika onderteken is
One of the threats is the ongoing exposure of organisms to environmental contaminants such as agricultural chemicals, factory waste and heavy metals from mining activities
Summary
Wat die gevolg kan wees van verskeie oorsake wat ekostelsels bedreig, verwys ekotoksikologiese risiko spesifiek na risiko wat die gevolg is van toksikologiese agense wat in die omgewing beland. Die ewekansige keuse van ’n toetsspesie as verteenwoordiger van ’n groep van spesies om die risiko vir die ekostelsel daaruit te probeer aflei, het sekere beperkinge tot gevolg omdat dit alle spesies gelykstel en ook nie met interaksies tussen spesies rekening hou nie. Verder moet onthou word dat sodanige aanpassing gewoonlik gepaard gaan met betekenisvolle veranderinge in die bevolkingsgenetiese struktuur wat veranderinge in alleel-/genotipe-frekwensie en algehele genetiese variasie beteken as gevolg van “bevolkingbottelnekke” of seleksie by sekere lokusse.[10] Of hierdie veranderinge, wat wel tot hoër toleransie lei maar meestal tot verlaagde variasie aanleiding gee, op die lange duur steeds as “suksesvol” getipeer kan word, is hoogs twyfelagtig omdat die spesie se stryd om oorlewing ten nouste van die omvang van sy genetiese variasie afhanklik kan wees. Dit word algemeen as realistiese uitgangspunt in omgewingsbeskerming en risikobepaling aanvaar dat risiko nooit heeltemal uitgeskakel kan word nie maar wel tot aanvaarbare vlakke beperk kan word
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