The Accumulation And Distribution Characteristics Of Cadmium And Copper In Earthworm Eisenia Fetida Under Combined Pollution In Soil

Earthworm is one of the largest soil animal groups in soil.It not only plays an irreplaceable role in maintaining the function of soil ecosystem,but also is an important indicator of soil pollution state.Earthworms are world-widely used for ecotoxicological risk assessment and Eisenia fetida is the most commonly used species.The pollutants can enter into the earthworm through the epidermis and intestine,and the main ways of different pollutants entering into the earthworm are different.The toxic effects of heavy metals on earthworms are related to their effects on different biological levels of earthworms.At present,it is generally to evaluate the toxicity of single heavy metal exposure in soil ecosystem.Due to the synergistic effect or enhancement effect of combined pollution will increase the risk of soil ecosystem.Therefore,it is urgent to comprehensively assess the impact of combined pollution on soil organisms.Cadmium and copper are important heavy mental elements.In order to provide a theoretical basis for the safety assessment of soil ecosystem,this study analyzed the biological indicators of earthworms under different treatments,studied the effects of single and combined pollution of cadmium and copper on the accumulation and distribution of copper and cadmium in earthworms under different intake pathways through soil exposure,earthworm sealing,and different concentrations of single and combined pollution of cadmium and copper.The main results are as follows:1.Cadmium(Cd)accumulation in earthworm was mainly affected by cadmium concentration and exposure time,oral sealing treatment significantly reduced the cadmium accumulation in intestine.Epidermal ingestion was the main way for cadmium intake.The epidermal ingestion of cadmium in the control treatment was accounted for 41.07% ～ 69.08%of the total cadmium intake,with an average of 57.40%.The epidermal ingestion of cadmium in the oral sealing treatment was accounted for 63.73%～79.69% of the total cadmium intake,with an average of 71.33%.The Cd accumulation in epidermal under control treatment was positively correlated with the protein concentration(Pr),the Cd accumulation in epidermal under oral sealing treatment was further correlated with the superoxide dismutase activity(SOD).The Cd accumulation in intestine under control treatment was correlated with the sulfydryl concentration(SH),the Cd accumulation in intestine under oral sealing treatment was positively correlated with the superoxide dismutase activity(SOD).2.Copper(Cu)accumulation in earthworm was mainly affected by copper concentration,oral sealing treatment significantly reduced the copper accumulation in intestine.Epidermal ingestion was the main way for copper entering into earthworm.The epidermal ingestionof Cu in the control treatment was accounted for 60.37%～79.76% of the total Cu intake,with an average of 72.87%.While the epidermal ingestion of Cu in the oral sealing treatment was accounted for 73.52%～97.40% of the total Cu intake,with an average of 84.89%.The Cu accumulation in epidermal under control treatment was correlated with the sulfydryl concentration(SH),the increased SOD activity accelerated the Cu accumulation in earthworm.The Cd accumulation in intestine under control treatment was correlated with the sulfydryl concentration(SH)and Pr content,the Cd accumulation in intestine under oral sealing treatment was positively correlated with the Pr content,and correlated with superoxide dismutase activity(SOD)under high Cu concentration exposure.3.Cadmium could inhibit the accumulation of copper in earthworm epidermis and intestine.With the increased addition of Cd,the accumulation of Cu in earthworm was subsequently reduced,especially in the epidermis.Oral sealing reduced the Cu accumulation in earthworm intestine.Cd addition reduced Pr content and SOD activity,while accelerated the SH concentration.The Cu accumulation in epidermal under control treatment was correlated with the Pr content and SOD activity.The Cd accumulation in intestine under control treatment was negatively correlated with Pr content.The Cd accumulation in epidermal under oral sealing treatment was positively correlated with the SOD activity,while the Cd accumulation in intestine under oral sealing treatment was negatively correlated with SH concentration and SOD activity.4.Low and medium concentration of copper(100 mg/kg、200 mg/kg)promoted the accumulation of cadmium in earthworm,while high concentration of copper(300 mg/kg)inhibited the accumulation of cadmium in earthworm.Cu addition could increase the Pr content,SH concentration and SOD activity.Under combined pollution,the Cd accumulation in epidermis was positively correlated with SH concentration,the Pr content and SOD activity.While the Cd accumulation in intestine was positively correlated with Pr content under control treatment,and not correlated with any of those indexes under oral sealing treatment.In conclusion,under this study,the addition of copper promoted the toxic effect of cadmium on earthworms,showing synergistic characteristics.The addition of Cd showed different toxic effects which was affected by Cu concentration.Under low Cu concentration,the effects were antagonism,while under high Cu concentration,the effects were synergism.Pollutant accumulation under the oral sealing treatment was lower than that under the control treatment.The mechanism of earthworm detoxification of combined cadmium and copper pollution was as follows: the earthworm produces a large amount of SH to absorb the excessive heavy metals,but with the increased concentration of heavy metals,the earthworm could possibly excrete the heavy metals for detoxification.