Iain Green

The bioavailability of Cd and Zn from soils amended with sewage sludge to winter wheat and subsequently to the grain aphid Sitobion avenae

Abstract An agricultural soil in southern England was amended with a single application of sewage sludge from a municipal source at rates of 0, 5, 7.5, 10, 15 and 20 t ha−1 dry solids. Soil concentrations of Cd and Zn in the field plots ranged from 0.109 to 0.180 mg kg−1 and 26.3 to 34.3 mg kg−1, respectively, dependent on sewage sludge application rate. Concentrations of Cd and Zn in the shoots of winter wheat grown were dependent on the rate of sewage sludge application to the soil. Concentrations of Cd in the ears of wheat were not dependent on sewage sludge application rate, whilst Zn concentrations were dependent. Grain aphids (Sitobion avenae) collected from the host plants accumulated concentrations of Cd and Zn up to 0.386 mg Cd kg−1 and 319 mg Zn kg−1 (eight and 10 times greater, respectively, than the concentrations on the ears on which they were feeding). Regression analysis demonstrated that the concentrations of Cd and Zn in S. avenae could be predicted from the concentrations of these metals in the soil. The retention characteristics of the sludge amended soils and control soils for Cd and Zn were assessed by batch adsorption experiments. From the sorption data it was observed that the sewage sludge amended soils showed no significant change in Cd affinity when compared to the controls soils. However, for Zn, the reduction in the Freundlich distribution coefficient of the isotherms of the sludge treated soils were significant when compared to the control soils — indicating a reduced affinity for Zn at these relatively low sewage sludge application rates.

Transfer of cadmium and zinc from sewage sludge amended soil through a plant–aphid system to newly emerged adult ladybirds (Coccinella septempunctata)

An agricultural soil was amended with sewage sludge at rates equivalent to 0, 10 and 30 t (dry solids) ha−1 and the subsequent transfer of zinc and cadmium through a soil–plant–arthropod system was investigated. Zinc concentration in soil, wheat and aphids increased significantly with sludge amendment rate. Zinc was biomagnified during transfer along the pathway, resulting in concentrations in the aphids four times greater than in the soil. Cadmium concentration in the soil was also significantly elevated by the addition of sludge, but there was no significant difference in cadmium concentration in the shoots of wheat plants. Cadmium concentration in aphids followed the pattern found in plants, but again, differences between treatments were not significant. Aphids collected from the plants were subsequently fed to fourth instar Coccinella septempunctata. Consumption of these aphids did not result in significant differences between treatments in the body burden of newly emerged adult C. septempunctata for either metal. Sequestration of cadmium in the pupal exuviae had a greater effect on the body burden of newly emerged adult ladybirds than for zinc. Results are discussed in relation to possible risks posed by the transfer of trace metals via the soil–plant–arthropod system to predatory arthropods.

Factors affecting the concentration in seven-spotted ladybirds (Coccinella septempunctata L.) of Cd and Zn transferred through the food chain.

The transfer of Cd and Zn from soils amended with sewage sludge was followed through a food chain consisting of wheat, aphids and the predator Coccinella septempunctata. Multiple regression models were generated to predict the concentrations of Cd and Zn in C. septempunctata. No significant model could be generated for Cd, indicting that the concentration of this metal was maintained within relatively narrow limits. A model predicting 64% of the variability in the Zn concentration of C. septempunctata was generated from of the concentration of Zn in the diet, time and rate of Zn consumption. The results suggest that decreasing the rate of food consumption is an effective mechanism to prevent the accumulation of Zn and that the availability of Zn in the aphid prey increased with the concentration in the aphids. The results emphasise the importance of using ecologically relevant food chains and exposure pathways during ecotoxicological studies.

The uptake of cadmium and zinc by the bird-cherry oat aphid Rhopalosiphum padi (Homoptera:Aphididae) feeding on wheat grown on sewage sludge amended agricultural soil.

A greenhouse trial investigated the uptake of cadmium and zinc by the bird-cherry oat aphid (Rhopalosiphum padi) feeding on wheat grown on sewage sludge amended soil. The trial was conducted at application rates of 0, 5, 7.5, 10, 15 and 20 tonnes ha(-1) dry solids. Concentrations of Cd and Zn were within current UK limits for potentially toxic elements in soils amended with sewage sludge. Cd and Zn in wheat plants were significantly greater than controls. Batches of aphids feeding on the wheat also showed a significant increase in the uptake of Cd and Zn. This study demonstrates a potential route of exposure to Cd and Zn for the predators of cereal aphids.

The tri-trophic transfer of Zn from the agricultural use of sewage sludge

Abstract An agricultural soil in Southern England was amended with two annual applications of sewage sludge at rates of 0, 10 and 15 t ha −1 dry solids. Soil concentrations of Zn reached 31.1 μg g −1 and the subsequent uptake was measured in wheat plants ( Triticum aestivum ), grain aphids ( Sitobion avenae ) and a predatory carabid beetle ( Bembidion lampros ) in order to test the hypothesis that Zn was transferred through this tri-trophic food chain. Concentrations of Zn in the wheat plants, aphids and predatory beetles reached 31.7, 116.0 and 242.2 μg g −1 dry wt., respectively. A potential exposure pathway from soil→plant→herbivore→predator was identified, the concentration of Zn in the predatory beetle being related to the amount of aphids eaten and sewage sludge application rate. The concentrations of Zn in the sludge-amended soils were all well within current UK regulation limits and the relevance of exposure pathways at sub-critical concentrations when considering metal loading rates for sewage sludge amended soils is discussed.

Time-response relationships for the accumulation of Cu, Ni and Zn by seven-spotted ladybirds (Coccinella septempunctata L.) under conditions of single and combined metal exposure

Accumulation, and therefore toxicity, of trace metals in invertebrates may be affected by potential interactive effects that can occur amongst different metallic elements. However, there is little data on the nature and effects of such interactions in terrestrial systems. This work reports the interactions among Cu, Ni and Zn during accumulation by the beetle Coccinella septempunctata. Test animals were treated with 500mgkg(-1) of each metal singularly and in combination for 15d. The effects of treatment with a single metal had no effect on the baseline concentrations of the other two. Time-response relationships for Cu and Ni after treatment with one metal were curvilinear, demonstrating that the metals were initially accumulated, but after ∼8d regulatory mechanisms became effective. This resulted in decreasing concentrations in test animals despite continued treatment. In contrast, the time-response relationship for Zn was linear. Treatment with metals in combination markedly altered the time-response relationships with all three metals showing a linear trend and the slope of the Zn relationship increasing significantly. After 15d of exposure this had the effect of increasing the metal concentration in animals exposed in combination compared to those exposed singularly by 144% to 38.3mgkg(-1) for Cu, 141% to 27.5mgkg(-1) for Ni and 55% to 311mgkg(-1) for Zn. For all metals, differences amongst treatments were significant, indicating that inter-element interactions can enhance the concentration of trace metals in C. septempunctata.

Feeding reduces waterborne Cu bioaccumulation in a marine rabbitfish Siganus oramin

Waterborne metal uptake has been extensively studied and dietary metal assimilation is increasingly recognized in fish, whilst the interaction between the two uptake routes is largely overlooked. This study compared the waterborne Cu bioaccumulation ((65)Cu as tracer) in a juvenile rabbitfish at different feeding regimes (starvation (SG), feeding normal diet (NDG) or diet supplemented with extra Cu (DCG)) to test the hypothesis that feeding can influence waterborne metal uptake in marine fish. NDG and DCG diet was fed as a single meal and then all fish were exposed to waterborne (65)Cu for 48 h, during which the time course sampling was conducted to determine (65)Cu bioaccumulation, chyme flow and dietary Cu assimilation. The results revealed that SG fish accumulated the highest (65)Cu, followed by NDG (61% of SG), whilst DCG fish accumulated the lowest (65)Cu (34% of SG). These results suggested a protective effect of feeding against waterborne Cu bioaccumulation. This effect was most notable between 10 min and 16 h when there was chyme in gastrointestinal tract (GT). Dietary Cu assimilation mainly occurred before 16 h after feeding. Waterborne (65)Cu influx rate in the GT was positively correlated with (65)Cu contents of chyme in NDG, whereas it was largely negatively correlated with (65)Cu contents of chyme in DCG. The waterborne Cu uptake in the GT was mainly influenced by the chyme flow and dietary Cu assimilation. Overall, our findings suggested that feeding has an important effect on waterborne metal uptake and that both the feeding status of the fish and the relative metal exposure through water and food should be considered in prediction of the metal bioaccumulation and biomonitoring programs.

Assessment of biotransfer and bioaccumulation of cadmium, lead and zinc from fly ash amended soil in mustard–aphid–beetle food chain

The present study investigates the extent of biotransfer and bioaccumulation of cadmium (Cd), lead (Pb) and zinc (Zn) from fly ash amended soil in mustard (Brassica juncea)-aphid (Lipaphis erysimi)-beetle (Coccinella septempunctata) food chain and its subsequent implications for the beetle. The soil was amended with fly ash at the rates of 0, 5, 10, 20 and 40% (w/w). Our results showed that the uptake of Cd, Pb and Zn from soil to mustard root increased with the increase in fly ash application rates, but their root to shoot translocation was relatively restricted. Increase in chlorophyll content and dry mass of mustard plant on treatments ≥20% even at elevated accumulation of Cd (1.67mgkg-1), Pb (18.25mgkg-1) and Zn (74.45mgkg-1 dry weight) in its shoot showed relatively higher tolerance of selected mustard cultivar to heavy metal stress. The transfer coefficient (TC1) of Cd from mustard shoot to aphid was always >1, indicating that Cd biomagnified in aphids at second trophic level. But, there was no biomagnification of Cd in adult beetles at third trophic level. Zinc accumulation was 2.06 to 2.40 times more in aphids than their corresponding host shoots and 1.26-1.35 times more in adult beetles than their prey (aphids) on which they fed. Lead was only metal whose TC was <1 at both second and third trophic levels. The elimination of Cd via honeydew of aphids was most efficient as the ratio of metal in honeydew to aphid (ranging from 0.21 to 0.26) was higher than the Pb (0.16 to 0.20) and Zn (0.07 to 0.09). The statistically consistent (p>0.05) biomass and predation rate of predatory beetles indicated that all levels of soil amendments with fly ash did not have any lethal or sub-lethal effects on beetles.

Assimilation of Cd and Cu by the carnivorous plant Sarracenia leucophylla raf. fed contaminated prey.

Many species of carnivorous plants have become endangered through exposure to multiple risks such as habitat loss, illegal poaching, and pollution. A potential threat to these plants posed by pollution stems from the contamination of their invertebrate prey with trace metals. This study examined the potential for prey to act as sources of the trace metals Cd and Cu for the pitcher plant Sarracenia leucophylla. Cd- and Cu-contaminated Diptera larvae were fed to S. leucophylla plants in separate experiments. The results demonstrated that Cd and Cu were readily transferred to the shoots of S. leucophylla in a dose-dependent manner. While the assimilation of Cu decreased with treatment level, the assimilation of Cd did not. Some assimilated Cu appeared to be translocated to the roots, but Cd was strongly retained in the shoots, where it was related to a reduction in shoot biomass. This suggested that on exposure to Cd-contaminated prey, the plants either experienced phytotoxicity or there was disruption of nutrient acquisition from the prey. Accumulation of Cu was not related to any sign of phytotoxicity.

Restoration in the face of climate change: a case study from the Dorset Heaths

This paper demonstrates the potential for restoring a range of habitats by comparing the efficacy of different techniques for restoring lowland dry Atlantic heathland in Dorset, UK, under current and future climatic conditions. The success of different treatments in reducing soil pH and concentrations of the most important macronutrient, phosphorus, on improved pasture adjacent to Hartland Moor National Reserve in Dorset are discussed. The treatments applied were soil removal, soil acidification using elemental sulfur, soil acidification using ferrous sulfate, and nutrient removal. The treatment that most successfully reduced extractable phosphate was soil removal. Nutrient removal produced no significant decrease in extractable phosphate over 7 years study. Soil acidification with sulfur most successfully reduced pH. Under the present climatic conditions, the elemental sulfur treatment produced far more abundant heather growth than soil removal. This study suggest that restoration techniques are likely to change in their relative effectiveness as climate changes and that this may have different consequences for low and high trophic level species.