Ecological relevance of suborganismal and population responses of terrestrial oligochaeta to the fungicide copper oxychloride

[摘要] ENGLISH ABSTRACT: Copper oxychloride is a fungicide that is extensively used in vineyards in the WesternCape to treat and prevent fungal diseases. It is however not clear what the effects areon soil organisms, which play an important role in soil fertility, in South African soils.There is paucity of data linking results obtained in the laboratory to effects observedin the field, which will only become useful if a clear relation can be demonstrated.The aims of this study were to:~ Determine the effects of copper oxychloride on field populations of earthwormsand simultaneously monitor lysosomal membrane stability, measured as neutralred retention time (NRRT).~ Validate experimental field studies by doing inventories of earthworm populationsin long-term sprayed vineyards.~ Determine the LC50 of copper oxychloride and simultaneously measuring NRRT,and linking them to the experimental field studies.~ Conduct bioassays, burrowing activity- and soil-avoidance experiments toinvestigate their relations to earthworm population responses in the experimentalfield studies.Earthworms were sampled by hand-sorting in the field tests on treated and untreatedfield plots in the Western- (October 1998 - July 1999) and Northern Cape (April 1998- October 1999). Soil samples and worms were analysed for copper contents andcoelomocytes of live earthworms were used to conduct the neutral red retentionassays.Acute toxicity tests were conducted over a period of 28 days during which theearthworms (Eisenia fetiday were exposed to different concentrations of copperoxychloride. Change in biomass and mortality were measured as endpoints, as well asNRRT.Bioassays, burrowing activity and soil-avoidance were conducted by exposingAporrectodea caliginosa to grassland- and vineyard soil as well as grassland soilspiked with 60 J.1g.g-1copper in the form of copper oxychloride. Growth andmortality were recorded in the bioassays as well as copper concentrations Inearthworm body tissues and substrates used over a period of28 days. Burrowing activity and soil-avoidance were determined by measuring the length oftunnels burrowed by A. caliginosa in soil profiles over a period of 4 days underdifferent exposure regimes.Results from the field tests showed that spraying of copper oxychloride had a negativeeffect on earthworm populations at the prescribed application rates. NRR T inearthworms from the exposure plots was significantly (p<0.05) lower after just onespraying application. It was concluded that spraying copper oxychloride at prescribedapplication rates caused a decrease in field populations of earthworms and that NRRTwas an early and reliable biomarker since it was indicative of later effects observed atthe population level. Results obtained from the field inventory of earthworms invineyards at Nietvoorbij, Robertson end Worcester confirmed data from the two fieldstudies.The calculated LC50 of 882.78 I1g.g-1 for copper oxychloride and 519.40 I1g.g-1 forcopper was ecologically relevant if a safety factor of 10 was applied. NRRT whichmanifested earlier than effects on biomass change in the acute toxicity tests, weresignificant when viewed against the background of responses of field populations ofearthworms.From the bioassay experiments it was found that A. caliginosa exposed to copperoxychloride spiked soil had significantly (p<0.05) higher weight loss and mortalitythan those in grassland- and vineyard soil. This indicated that changes in biomass andmortality were indicative of population responses in the field and can be considered asecologically relevant.Burrowing activity of A. caliginosa was significantly (p<0.05) lower in vineyard andcopper oxychloride spiked soil than in grassland soil. Similarly in the soil avoidanceexperiments it was found that A. caliginosa avoided vineyard- and copper oxychloridecontaminated soil. It is therefore concluded that burrowing activity and soilavoidance were ecologically relevant endpoints since they corresponded withpopulation responses in the field.The study thus revealed that the long-term usage of copper oxychloride could havenegative effects on earthworm populations. The spraying of copper oxychloride canhave important implications on the sustainable use of agricultural soils sinceearthworms and other soil organisms play such an important role in soil fertility. Theuse of biomarkers and other ecotoxicological indicators can provide an early warningthat soil organisms are under environmental stress.

[发布机构] Stellenbosch University