Study Of The Ecology Toxic Effects Of Single And Combined Pollution Between Heavy Metal And Glyphosate

Herbicide glyphosate (GPS) is widely used in the environments, including farmland andorchard, where heavy metals are very often found in elevated levels. Co-existence of metal andGPS could result in combined pollution of soil environment. Furthermore, GPS affects metalbehaviors in water and soil systems because its functional groups such as amine, carboxylate andphosphonate react with metal ions to form metal complexes.(1) A laboratory experiment was therefore conducted to investigate the interactions of GPSand Cu or Cd with respect to acute toxicity to Photobacterium phosphorem T3. Photobacteriumwere exposed to the solution containing different concentration Cu or Cd and GPS. Then theEC50(Median Effective Concentrations) of GPS and Cu or Cd were measured based on linearregression analysis. To study the combined effects, photobacterium were exposed to the solutionscontaining different concentrations of Cu or Cd at the different GPS concentrations, the inhibitionof photobacterium was calculated. Results showed that the toxicity of Cu or Cd tophotobacterium was much higher. The GPS (technical-grade glyphosate acid), unadjusted pH,possessed much higher toxicity. Because GPS is a Lewis acid, the adding of this acid decreasedthe pH of the test media obviously. Nevertheless, toxicity of GPS (pH adjusted) was not observedin this study. Additionally, the presence of GPS could significantly reduce the acute toxicity ofCu or Cd to photobacterium. Particularly, the inhibition to photobacterium decreasedsignificantly wih the increase molar ratio value of GPS/Cu. Based on the observations of thepresent study, it can be concluded that that Cu or Cd exhibited acute toxicities on photobacterium,the toxicity increased when Cu or Cd concentration increased. However, GPS was nearlynon-toxic to them and the presence of GPS could significantly reduce the acute toxicity of heavymetal on photobacterium. Buffered medium or pH-adjustment should be included in the toxicitytests for acidic toxicants to eliminate pH-induced toxicity since natural soil and water has higherbuffering capacity than test media in resisting pH change.(2) A laboratory experiment was conducted to investigate the interactions between GPS andcopper (Cu) expressed with the acute toxicity of soil invertebrate earthworm (Eisenia fetida),which was exposed to aqueous solutions for48h with different mixing concentrations of Cu andGPS (technical-grade Gly acid). The mortality rates, Cu uptake by earthworm, and somebiomarkers such as superoxide dismutase (SOD) activity, glutathione (GSH) content, andacetylcholinesterase (AchE) activity were measured. The mortality rates and whole-worm metalburdens increased significantly with the increasing exposed concentration of Cu. However, therewas no indication that GPS was toxic to earthworms in this study. Furthermore, the presence of GPS could significantly reduce the acute toxicity of Cu to earthworms. The mortality ratesdecreased sharply and the uptake of Cu was nearly halted in the presence of GPS. In addition tothat, the SOD activity, GSH content, and AchE activity almost declined to the levels of thecontrol. These results demonstrate that GPS could control the toxicity as well as thebioavailability of heavy metals in soil solutions where both GPS and heavy metals often coexist.(3) Glyphosate (GPS) is a wildly used pesticide throughout the world. It affects metalbehaviors both in water and soil system because its functional groups such as amine, carboxylateand phosphonate can react with metal ions to form metal complexes. As a result, GPS cantypically decrease the heavy metal bioavailability. A laboratory experiment was conducted toinvestigate the interactions between GPS and copper (Cu) with respect to the subacute toxicity tosoil invertebrate earthworm (Eisenia fetida). Earthworms were exposed to artificial soil for28dwith different concentrations of Cu and GPS (technical-grade GPS acid). The growth inhibitionratio, cocoon production, Cu uptake by earthworm, and some biomarkers such as superoxidedismutase (SOD) activity, catalase (CAT) activities, and malondialdehyde (MDA) content weremeasured. The growth inhibition ratio and whole-worm metal burdens increased significantlywith the increasing exposed concentration of Cu. However, the toxicity of GPS was much lowerthan copper in this study. Furthermore, The joint toxicity data showed that the presence of GPScould reduce the toxicity of Cu to earthworm, The growth inhibition were alleviated obviously,the cocoon production were increased, and Cu absorption by earthworms were decreased. Inaddition, the SOD, CAT and MDA were alleviated by Cu when GPS was present to a certaindegree. Therefore, it is shown that the herbicide glyphosate can affect the toxicity andbioavailability of heavy metals in the soil ecosystems acts.This may be due to GPS is similar tothe well-known complexing agents for Cu like EDTA and NTA.(4) A laboratory experiment was therefore conducted to investigate the interactions of GPSand Cd with respect to acute toxicity to earthworm (Eisenia fetida). To study the combinedeffects, earthworm were exposed to the solutions containing different concentrations of Cd at thedifferent GPS concentrations. Results showed that the toxicity of Cd to earthworm was muchhigher. The presence of GPS could significantly reduce the acute toxicity of Cd to earthworm.Particularly, the motility, accumulation of Cd decreased significantly wih the increase molar ratiovalue of GPS/Cd. Analyses of metal subcellular distribution in E. fetida showed that the theinternal metals Cd were major in fraction E (intact cells), H (heat-stable proteins fraction),followed by the G (denatured proteins fraction), F (microsomal fraction), D (microsomalfraction). In the presence of GPS, each fraction, especially the fraction E, were decreased to acertain extent, respectively. In addition to that, the SOD activity, CAT activity, and GSH-Pxactivity also declined. Based on the observations of the present study, it can be concluded that,GPS was nearly non-toxic to them and the presence of GPS could significantly reduce the acutetoxicity of Cd on earthworm.(5) A laboratory experiment was conducted to investigate the interactions between GPSand Cd with respect to the subacute toxicity to soil invertebrate earthworm (Eisenia fetida). Earthworms were exposed to artificial soil for28d with different concentrations of Cd and GPS(technical-grade GPS acid). The weight loss ratio, cocoon production, Cd uptake by earthworm,and malondialdehyde (MDA) content were measured. The weight loss ratio, cocoon production,whole-worm metal burdens, MDA content were all changed significantly with the increasingexposed concentration of Cd. Furthermore, the joint toxicity data showed that the presence ofGPS could reduce the toxicity of Cd to earthworm. The growth inhibition were alleviatedobviously, the cocoon production were increased, and Cd absorption by earthworms weredecreased. In addition, the MDA were alleviated by Cd when GPS was present to a certain degree.Therefore, it is shown that the herbicide glyphosate can affect the toxicity and bioavailability ofCd in the soil ecosystems acts.