Pedochemical Studies On Some Soils Of Egypt With Special Reference To Some Heavy Metals:

Omar Hssieny Mohamed Ei-hussieny

The aim of this investigation was to study (i) the effect of usingsewage eflluents and industrial waste water in irrigation on the physical andchemical properties of soil and its content of Cu, Zn, Pb, Cd, Ni and Co, (ii)the effect of industry fall-out derived from some chemical plants and smelterson the status of the tested heavy metals in the neighboring soils, (iii) the effectof motor vehicle exhausts on the total and forms of heavy metals in theroadside soils, and (iv) the contamination of plants with the above mentionedheavy metals.To achieve the first objective, three locations in El-Gabal El-Asfarrepresent soils irrigated with sewage eflluents for 0, 20 and 60 years andanother two locations at Bahteem representing soils irrigated with indu~trialwaste water were selected. Soil samples from five different depths from eachprofile namely, 0-5, 5-10, 10-25,25-60 and 60-100 em and correspondenceplant samples were collected.To accomplish the second objective, five different chemical plants andsmelters were selected and two profiles were dug around the source, the firstone was on a 5m away and the second was 100m away from the source ofpollution. Soil samples were taken from the different depthes as mintionedabove and samples from the plants grown on the different locations werecollected.The third objective was fulfilled through collecting soil and plant•samples from six locations differing in their distance and direction from themotor way.The physical and chemical properties of selected soils weredetermined. The total content, DTPA-extractable and fractions of Cu, Zn, Pb,Cd, Ni and Co in soil samples were measured. The fourth objective waslargely met through the determination of heavy metals in plant samples. Theobtained results could be summarized as follows:The effect of using sewage effiuentes and industrial waste water inirrigation on the physical and chemical properties of soils was obvious and themost affected soil properties were soil organic matter, soil pH, CEC,exchangeable cations and total soluble salts, wherase the other properties wereless affected. With increasing the peroid of irrigation, soil organic matter wasincreased, but soil pH and total soluble salts were decreased.l-Coppersoil content of copper was relatively high in soils received sewagewater for 60 years and ranged from I to 475 mglkg soils, DTPA-extractableCu varied from 0.1, to 24.4 mglkg soil, while the distribution of Cu amongvarious fractions followed the following order:Residual > organically bound (Cu~PYR> Occluded on Fe, AI and Mn Oxides(Cu-Ox + Cu-meA + Cu-HAH) > specifically adsorbed (Cu-AC» soluble +exchangeable (Cu-CA).Copper in soils exceeded the maximum tolerable level in site 3irrigated with sewage water for 60 years, as well as in sites 4 and 5 irrigatedwith industrial waste water. However, in soils around smelters, the content ofCu was comparable with that of the maximum tolerable level. Theconcentration of Cu in the correspondence plants grown on soils irrigatedfor60 .years, soils around smelters and soils adjacent to the highway tended to betoxic.2-ZinCiThe content of zinc in soils was generally high easpecially in soils ofEl-Gabal El-Asfar. Total Zn ranges from 11to 1075mg/kgsoil, while DTPAextractableZn being from 0.22-5000 mg/kg soil. The distribution of Znamong the chemical fractions was followed this order: Residual> Organicallybound> Occluded on Fe, AI and Mn Oxides> specifically adsorbed> soluble+ exchangeable.Total Zn in soils surpassed the maximum tolerable level in profile 3(soils irrigated with sewage effiuents for 60 years), while around the smelters(profiles 12,13), the concentration of Zn was relatively high and beyond themaximum level (30 mg/kg). Zn concentration in the growing plants was withinthe permissible level with a slight increase in those grown on soils irrigatedfor 60 years.3-LeadiTotal Pb in soils and DTPA-extractable Pb ranged from 13 to 226 andfrom 0.02 to 19.0 mg/kg, respectively. The distribution ofPb among thedifferent chemical forms followed this order, Residual > PYR > specificadsorbed> Occluded on Fe, AI and Mn oxides> soluble + exchangeable.Total Pb in soils around the chemical plants and in those adjacent tothe highway is still within the permissible level. However, in soils irrigatedwith sewage effiuents for 60 years (profile 3), Pbhas exceeded the thresholdvalue of 100 mg/kg soil.Soils of profiles 4 and 5 irrigated with industrial waste waters contain highamount ofPb comparable to that reported as threshold value (100 mglkg soil).The concentrations of Pb in plants grown on soils irrigated with sewageeffiuents were highly polluted especially in profile (3). Plants grown on soilsadjacent to the highway contained higher amounts of Pb and there is atendency to reach the higher level of the critical toxicity range (10-20 ug/g).4-Cadmium:Cadmium content in soils was generally high in all investigated soils.Total Cd content ranged between 3.0 to 13 mglkg soil, while DTPAextractableCd varies from 0.01 to 1.4 mg/kg soil.Total Cd in the investigated soils was surpassed the limited reported tobe maximum tolerable level (5 Ilg/g)·The occurrence of Cd in the different chemical fractions followed thisorder: Residual> soluble + exchangeable> organically bound> Occluded onFe, Al and Mn oxides. > specifically adsorbed, which means that Cd is moreleachable and mobile than the other elements.Concerning the concentration of Cd in plants grown on soils irrigatedwith sewage effiuents for 60 years (profile 3), it was increased lind tended toreach the toxic level. Plants grown on soils irrigated with industrial wastewater contain high Cd concentration very close to levels of the toxicity range.However, those grown on the other locations contain high concentration of Cdlocated within the critical toxicity range (5-10 Ilg/g)·5-Nickel:The content of Ni in soils ranges between 4.4 and 16~ mg/kg soil,while DTPA-extractable Ni varied from 0,01 to 1.4 mglkg.The distribution of Ni among the fractions followed the order of:Residual> specifically adsorbed> occluded on crystalline Fe and AI oxidesorganically bound> soluble + exchangeable> Occluded on amorphous Fe andAI oxides.The threshold value (100 mglkg) was exceeded by the total Ni in soilsirrigated with industrial waste water (profiles 4,5) and in soils around smelters(profiles 12,13). Total Ni content in profiles (16 and 17) located on the eastside of the road as well as in profiles 19 and 20 located on the waste sidesurpassed the thresold value.The concentration of Ni in plants grown on the soils irrigated withsewage and industrial waste water was high, but still less than the level oftoxicity. The Ni contents in plants grown on soils around the chemicalfactories or on soils adjacent to the highway are not harmful to animals.6-CQbalt:Total Co content in soils ranges from 19 to 59 mglkg soil, and theDTPA-extractable Co varies from 0.16 to 1.43 mglkg soil.The distribution of Co among the fractions was followed this order:Residual> organically bound> Occluded on Fe and AI, oxides> specificallyadsorbed> soluble + exchangeable.Total Co content in soils was affected by sewage and industrial waste .water, industry fallout and the motor vehicle exhaust fums.Plants grown on soils irrigated with sewage etnuents for 60 yearscontain high level of Co comparable to that of critical toxicity range. On theother hand, those grown on soils around chemical plants and smelters, orgrown on soils adjacent to the highway contained less Co and their contentsdid not exceed that of the toxicity level.The following remarks could be eeneludede1- Soils irrigated with sewage effluents are seriausly contaminated with Cu,Zn, Pb and Cd. Generally these heavy metals in addition to Ni and Cowere increased with increasing the period of irrigation with sewageetnuents and tended to decrease with soil profile depth.2- The heavy metals were relatively high in soils around the chemical plantsand smelters. Moreover, the content of Cu, Pb, Zn, Cd, Ni was high andexceeded the permissible level only in soils around smelters..3- Soils adjacent to the highway contain relatively high concentrations ofheavy metals which exceeded the permissible levels in some locations.Generally, the concentration of heavy metals decreased with increasingboth of distance from the road and profile depth.