A.J. Reinecke

The suitability of Eudrilus eugeniae, Perionyx excavatus and Eisenia fetida (Oligochaeta) for vermicomposting in southern Africa in terms of their temperature requirements

Abstract Since the epigeic species Eudrilus eugeniae, Perionyx excavatus and Eisenia fetida have a potential as waste decomposers or as possible sources of protein, knowledge of their temperature requirements are required in order to cultivate them in large numbers under different environmental conditions. A study was undertaken outdoors as well as indoors of earthworm populations in artificial containers in order to access the influence of high, as well as low, temperatures on the different species. The results were compared with that obtained for control populations kept at a presumably favourable temperature of 25°C. The results showed that Eisenia fetida has a wider tolerance for temperatures than E. eudrilus eugeniae and P. excavatus which allows this species to be cultivated in areas with higher temperatures (often as high as 43°C) as well as areas with lower soil temperatures (often below 5°C). The other two species will have limited outdoor application in vermiculture systems. The winter temperatures in the southern subregion of Africa and not the summer temperatures seem to be the limiting factor in applying Eudrilus eugeniae and P. excavatus in outdoor vermiculture. The incubation period, development and cocoon production of the species at various temperature simulations were also investigated. Regions in southern Africa were identified, based on prevailing temperature conditions, where E. eugeniae and P. excavatus could be utilized in vermiculture systems.

Runoff-related pesticide input into the Lourens River, South Africa: basic data for exposure assessment and risk mitigation at the catchment scale

The characterization of runoff-related pesticide input and the identification of areas of concern in the field are essential for a comprehensive assessment of risk and the planning of mitigation measures. To this end, the agriculturally-derived aqueous and particle-associated pesticide contamination of the Lourens River and its tributaries was measured in a comprehensive design. Sampling was performed in the beginning of April prior to the first rainfall of the wet season and in the middle of April during high water conditions following the first rainfall of 9.6 mm d-1. Pre-runoff samples indicated contamination with endosulfan at levels up to 0.06 μg L-1, while no other pesticides were detectable. Rainfall-induced runoff resulted in an increase in the levels of the pesticides endosulfan, deltamethrin, azinphos-methyl, chlorpyrifos, and procymidone up to levels of 0.35, 1.4, 0.6, 0.19 and 9 μg L-1, respectively in water samples. Endosulfan, azinphos-methyl, and chlorpyrifos were detected at maximum concentrations of 273, 152, and 245 μg kg-1 in suspended sediments. No increased pesticide levels were detected at a control site upstream of the agricultural area. The Lourens River received its contamination via the tributaries discharging the surrounding farming area. Contamination of the six tributaries depended on landuse and slope characteristics and enabled the identification of target sites for risk reduction approaches. Transient pesticide levels exceeded the target water quality limit proposed by the South African Department of Water Affairs and Forestry (DWAF). The Lourens River site downstream of the farming area has been identified as a site where potential toxic conditions could arise.

Predicting runoff-induced pesticide input in agricultural sub-catchment surface waters: linking catchment variables and contamination

An urgent need exists for applicable methods to predict areas at risk of pesticide contamination within agricultural catchments. As such, an attempt was made to predict and validate contamination in nine separate sub-catchments of the Lourens River, South Africa, through use of a geographic information system (GIS)-based runoff model, which incorporates geographical catchment variables and physicochemical characteristics of applied pesticides. We compared the results of the prediction with measured contamination in water and suspended sediment samples collected during runoff conditions in tributaries discharging these sub-catchments. The most common insecticides applied and detected in the catchment over a 3-year sampling period were azinphos-methyl (AZP), chlorpyrifos (CPF) and endosulfan (END). AZP was predominantly found in water samples, while CPF and END were detected at higher levels in the suspended particle samples. We found positive (p < 0.002) correlations between the predicted average loss and the concentrations of the three insecticides both in water and suspended sediments (r between 0.87 and 0.94). Two sites in the sub-catchment were identified as posing the greatest risk to the Lourens River mainstream. It is assumed that lack of buffer strips, presence of erosion rills and high slopes are the main variables responsible for the high contamination at these sites. We conclude that this approach to predict runoff-related surface water contamination may serve as a powerful tool for risk assessment and management in South African orchard areas.

Uptake and distribution of Lead (Pb) and Cadmium (Cd) in the freshwater crab, Potamonautes perlatus (Crustacea) in the Eerste River, South Africa

The uptake and distribution of lead (Pb) and cadmium (Cd) in thefreshwater crab, Potamonautes perlatus in the Eerste River,South Africa were studied seasonally over two years by comparingconcentrations in crabs, water and sediment in two localities, one upstream and one downstream from the town of Stellenbosch. Lead and cadmium concentrations in whole crabs of different sizeclasses as well as concentrations in various organs and tissues were determined by atomic absorption spectrometry. Data on physical, chemical and bacteriological features are also presented. The mean Zn concentration in the sediment of the downstream locality (77.5 ± 38.4 μg g-1) was significantly higher than in the less polluted upstream locality(44.7 ± 32.8 μg g-1) whilst the manganese concentration of the sediment was significantly higher in the upstream locality. The gonads (mean Pb 23.4, range 0.1-125.0 μg g-1; mean Cd 5.3, range 0.1-22.2 μg g -1) and carapace (mean Pb 23.4, range 0.7-327.6 μg g-1; mean Cd 4.0, range 0.4-18.5 μg g-1) contained thehighest concentrations of both metals irrespective of season orlocality. For both Pb and Cd significant differences (p < 0.05, Students t-test) were found between the metal content of different organs. The gonads had the highest and the digestiveglands the lowest concentrations of both heavy metals.Results indicated that anthropogenic activities did not influencesediment and water concentrations significantly. Smaller crabs accumulated more lead and cadmium than larger crabs with all crabs having significantly higher concentrations than both waterand sediment. No significant differences in mean concentrationsof lead and cadmium in whole crabs or organs were found between the two localities. Although body loads for both metals did notreflect prevailing environmental levels of these metals reliably,the crabs may still be used to monitor bioavailability over time.

Cocoon production and viability as endpoints in toxicity testing of heavy metals with three earthworm species

Summary This study compares the cocoon production and cocoon viability of three earthworm species, Eudrilus eugeniae, Perionyx excavatus and Eisenia fetida after exposure to a sublethal concentration of lead nitrate. Cocoon production in all three species did not differ significantly between exposed and control worms. However, cocoon viability in all three species was affected detrimentally by the presence of lead nitrate. Cocoons of Eisenia fetida from substrates contaminated by lead nitrate, cadmium sulphate and zinc sulphate for 36 months, also showed a lowered cocoon viability. It is concluded that cocoon viability may be a sensitive endpoint of sublethal toxicity of these metal salts.

The influence of lead and manganese on spermatozoa of Eisenia fetida (Oligochaeta)

The effects of lead and manganese on the spermatozoan ultrastructure of Eisenia fetida were studied by feeding pre-clitellate worms in laboratory cultures weekly with fresh, urine-free cattle manure containing sublethal quantities of the heavy metal compounds for 8 weeks. The worms were analysed for heavy metal content after eight weeks, and electron microscopical observations of spermatozoa of exposed and control worms were performed. The body loads of heavy metals in the worms at the end of the observation period were 41.8 μg g−1 (0.20 μmol g−1) and 9.3 μg g−1 (0.17 μmol g−1) for Pb and Mn respectively, possibly indicating differential accumulation of the two metals since higher dosages of Pb were given. Electron microscopical observations showed marked cellular damage to the spermatozoa from worms exposed to the heavy metals, compared to the sperm cells from the control worms. Structural damage of spermatozoa included breakage and loss of nuclear and flagellar membranes, thickening of membranes, malformed acrosomes and loss of nuclear material. The fact that the spermatozoa were adversely affected by sublethal concentrations of certain heavy metals, raises the possibility of utilizing this phenomenon in toxicity testing.

Linking lysosomal biomarker and population responses in a field population of Aporrectodea caliginosa (Oligochaeta) exposed to the fungicide copper oxychloride

The effects of the fungicide copper oxychloride on a field population of the earthworm Aporrectodea caliginosa were investigated. Changes were monitored in earthworm numbers and biomass, copper concentrations in soil and earthworms, and neutral red retention times (NRRTs) of coelomocytes. The aim was to establish whether the cellular responses could be linked to changes at the population level. Results indicated that there was a significant (P<0.05) impact on worm density and biomass on the treated plots 6 months after spraying with the fungicide stopped. NRRTs of treated earthworms were significantly lower after one spraying when earthworms had elevated concentrations of copper in their body tissues. Six months after spraying stopped, copper levels in both soil and earthworm tissues declined significantly, but the earthworm numbers and biomass were still significantly lower in the treated plots. This indicated that the effects of the copper oxychloride exposure manifested at a much later stage at the population level, than on NRRT. We conclude that the decrease in NRRTs, which preceded the decrease in both earthworm biomass and numbers, may have predictive value as a biomarker of impending population changes.

The relationship between lysosomal biomarker and organismal responses in an acute toxicity test with Eisenia Fetida (Oligochaeta) exposed to the fungicide copper oxychloride.

The LC50 of copper oxychloride for Eisenia fetida was determined, and its effects on biomass change and lysosomal damage using neutral red retention times (NRRT) of coelomocytes were measured. The aim was to establish whether a lysosomal subcellular response, measured as NRRT, could be linked to the LC50 and biomass changes. Further, we attempted to establish the ecological relevance of the LC50 by comparing it to studies previously carried out on the effects of copper oxychloride on field earthworm populations. The experiment was conducted over a period of 28 days, during which the earthworms were exposed to different concentrations of copper oxychloride in artificial soil. The calculated LC50 was 883 microg g(-1) for copper oxychloride and 519 microg g(-1) for copper. Results indicated that changes in coelomocyte membrane stability manifested earlier than effects on biomass. Since the NRRT assay was very sensitive and generated an early response before changes in biomass or mortality could be measured, it may have predictive value and may contribute information during acute toxicity tests, which could be of greater ecological relevance than mortality data alone.

Avoidance behaviour of two eco-physiologically different earthworms (Eisenia fetida and Aporrectodea caliginosa) in natural and artificial saline soils

We studied the avoidance behaviour of Eisenia fetida and Aporrectodea caliginosa in OECD artificial soil spiked with NaCl and in natural saline soil (of varying ionic constitutions) collected from Robertson Experimental Farm (ROBS) in Western Cape, South Africa. For each organism, the ecotoxicological test was performed using a two-chamber test over a period of 48 h. The results showed that in the OECD soil, the avoidance EC50 (the concentration/electrical conductivity at which there is effect on 50% of the organisms) for A. caliginosa of 667 mg kg(-1) NaCl was lower than 1164 mg kg(-1) for E. fetida. Similarly in ROBS soil, the avoidance EC50 for A. caliginosa of 0.26 dS m(-1) was lower than 0.56 dS m(-1) in E. fetida. These results indicated that A. caliginosa showed better avoidance to salinity than E. fetida irrespective of soil types or ionic constitution. When compared with literature data, EC50 values in avoidance tests were either lower or comparable to those of reproduction, which was the most sensitive life-cycle parameter. The only exception was the EC50 value for avoidance of E. fetida in natural soil which was higher than for reproduction suggesting that the predictive value of the avoidance test for this species might be lower in natural soils. The variation in sensitivities of these earthworms could be as a result of differences in their eco-physiology. These findings suggest the relevance of the avoidance test as a suitable screening method showing first tendencies of saline stress on the habitat function of soils.

The temperature requirements of the epigeic earthworm species Eudrilus eugeniae (oligochaeta) — a laboratory study

Juvenile specimens of the epigeic earthworm species, Eudrilus eugeniae were subjected to a range of different constant temperatures in a temperature gradient trough over a period of 80 days. Other environmental factors and food availability were maintained at a constant, optimal level. Survival, growth rate, maturation and cocoon production were monitored regularly. No worms survived at temperatures < 12°C and all succumbed after 50 days at temperatures of 30°C and above. A steady increase in growth rate was observed with higher temperatures and the highest mean biomass per worm was attained at 29°C. The highest maturation rate was obtained at 22 and 25°C was found to be the optimal temperature for cocoon production. The results indicate that this earthworm species is very sensitive to low temperatures and can survive temperatures up to 30°C. It was also noted that although higher temperatures favoured growth, fecundity would be higher at temperatures ranging from 22 to 25°C. It is concluded that this earthworm species would be a better candidate for vermiculture in regions with a tropical or moderate climate as it exhibited a fairly narrow tolerance range for temperature with a high degree of intolerance for temperatures below 16°C.