Risk assessment of heavy metal contamination in soil and wild Libyan jird Meriones libycus in Riyadh, Saudi Arabia

This study was undertaken to document the impact of heavy metal pollution on the Libyan jird, Meriones libycus and to contribute to an environmental impact statement for the rapidly growing City of Riyadh. All metal concentrations in surface soil of a polluted site (within Riyadh City) were higherthan those from a reference site (outside the city).Although Pb declined versus earlier reports on Riyadh soil, Cd (0.97 microg g(-1)) and Hg (0.28 microg g(-1)) were above some of the most stringent quality guidelines (0.07-0.62 microg g(-1) for Cd and 0.14-0.18 microg g(-1) for Hg). Metal distribution in M. libycus proved site-related and organ-specific, recognizing a higher affinity of most tested metals towards the kidneys, liver and brain than the lung and heart. The comparatively lower site-specific accumulation of Pb in soft tissues was attributed primarily to its major hypothetical accumulation in bones, whereas, the transition rate of Hg from the liver was suggested to be lower to the brain than to the kidneys. Although a non hazardous status was assumed for Cu (11.27-13.16 microg g(-1)) and Hg (up to 0.207 microg g(-1)) in tissues of M. libycus, a potential risk was imposed by mean tissue concentrations of Cd (up to 3.29 microg g(01)), Ni (up to 1.48 microg g(-1)) and Pb (up to 1.94 microg g(-1)). On the grounds of the significantly higher metal levels in polluted soft tissues versus reference subjects, Libyan jirds possess high exposure potential and can be useful biomonitors of environmental metal contamination.     

镉胁迫对不同水稻品种幼苗根系形态和生理特性的影响

为了解植物根系对重金属镉的反应,以水稻秀水63和秀水09为试验材料,采用溶液培养方法,研究不同浓度镉(0、1、5、10、25、50、100 μmol·L~(-1))对水稻幼苗根系形态和部分生理特性的影响.结果表明:1 μmol·L~(-1)镉处理对2个水稻品种根系生长有一定的促进作用,表现为植株干质量、根系总长度、根系表面积、根体积和根系活力均略有升高.但随着镉浓度(5～100 μmol·L~(-1))增加,表现出一定的抑制效应,与对照相比,秀水63和秀水09分别在10 μmol·L~(-1)和25 μmol·L~(-1)镉处理时的根系干质量、根系总长度、根系表面积、根体积和根系活力明显受到抑制,而根系平均直径、质膜透性均有所增加.不同浓度镉胁迫对两个水稻品种直径≤1.5 mm的根系生长影响最大,其中高于10 μmol·L~(-1)镉胁迫下,秀水63直径≤1.5 mm根系长度、根系表面积和根系体积分别降低了11.89%～55.39%、10.77%～57.27%和18.37%～67.35%,秀水09分别降低了6.84%～40.48%、8.55%～42.79%和16.50%～52.42%.本实验结果表明,2个水稻品种对镉胁迫存在着一定的差异,秀水09对Cd胁迫的耐受能力要强于秀水63.     

改良剂对红蛋植物修复污染土壤重金属铅和镉效果的影响

通过盆栽试验研究了在重度重金属混合污染土壤上,施用不同配比的石灰和泥炭（T1,泥炭0 g·kg^-1土,石灰2 g·kg^-1土;T2,泥炭30 g·kg^-1土,石灰0 g·kg^-1土;T3,泥炭50 g·kg^-1土,石灰0g·kg^-1土;T4,泥炭30 g·kg^-1土,石灰2g·kg^-1土;T5,泥炭50 g·kg^-1土,石灰2g·kg^-1土）对红蛋（Echinodorus osiris）生长及其去除污染土壤铅、镉量的影响,探讨了化学修复和植物提取修复技术相结合修复重金属污染土壤的可能性。研究结果表明,施用石灰显著提高了土壤pH,施用泥炭不显著;施用石灰和泥炭后土壤中交换态铅、镉含量较CK显著降低,红蛋地上部和地下部铅、镉含量较CK有不同程度降低,T4、T5处理降低不显著;T3、T4、T5处理显著地提高了红蛋的铅单株迁移量和年迁移量,年迁移量分别为CK的2.1倍、2.6倍和2.8倍;T1、T2、T3、T4、T5处理显著地提高了红蛋的镉单株迁移量和年迁移量,年迁移量分别为CK的1.8倍、2.9倍、2.9倍、2.8倍和2.9倍,其主要原因在于施用土壤改良剂改善了红蛋的生长,显著增加了地上部生物量。结合经济效益方面因素考虑,以施用泥炭30g·kg^-1土和石灰2g·kg^-1土的处理更适合推广运用。     

改性污泥对矿区铜、镉污染土壤的修复

城市污泥的重金属含量超标是限制其资源化利用的主要瓶颈,论文采用石灰＋硫粉＋生物淋滤的方法去除重金属,制备改性污泥,探讨其对矿区Cu、Cd污染农田土壤的修复效果,以期实现以废治污的目标。供试水稻土采自江西某矿区附近农田,土壤Cu和Cd的TCLP（Toxicity characteristic leaching procedure）浸出量分别为40.34 mg·kg-1和660.1μg·kg-1,其中Cu的质量分数超过国际标准值15 mg·kg-1。通过室内土培的方法,将改性污泥分别按土重的0%、1%、3%、5%和10%施入供试土壤培养30 d后,分析土壤Cu和Cd的活性、形态变化以及土壤蛋白酶和脲酶活性等指标评价改性污泥对污染土壤的修复效果及作用机理。结果表明,改性污泥对土壤Cu产生显著的钝化作用,且各施用量对Cu的有效态含量表现出显著差异。当改性污泥的用量为土重的5%时,Cu的有效态含量降至12.03 mg·kg-1,低于国际标准。改性污泥对土壤Cd的钝化效果相对较弱。当改性污泥的用量为1%时,土壤Cd的活性反而有所增加。当改性污泥的用量为5%时,Cd的活性显著降低,土壤Cd的浸出量降至539.6μg·kg-1。土壤重金属形态分析的结果表明,土壤Cu主要以碳酸盐结合态、有机结合态和残渣态存在。改性污泥用量增加,可交换态Cu含量下降,当改良剂用量为土重的5%时,可交换态Cu由8.10%降至4.10%。相反,有机结合态Cu含量由26.45%增加至32.34%。土壤的可交换态Cd含量由36.80%降至30.69%。说明施用改性污泥,土壤可交换态Cu、Cd向有机结合态发生转化。土壤蛋白酶和脲酶的活性变化能较好地指示修复效果,且土壤脲酶的指示效果优于蛋白酶。     

石灰氮对镉污染土壤中镉生物有效性的影响

以石灰作对比,在大田条件下研究了不同石灰氮用量对镉污染土壤中镉生物有效性的影响。结果表明,一定量石灰或石灰氮处理均能显著提高酸性土壤的pH值,降低污染土壤中有效态镉质量分数及水稻茎叶和糙米中的镉质量分数。与不施改良剂的对照相比,石灰施用量达到1 200 kg.hm-2时土壤pH值显著提高,土壤有效态镉质量分数降低12.6%（P〈0.05）,水稻茎叶和糙米中镉质量分数分别降低25.5%（P〈0.05）和28.3%（P〈0.05）;石灰氮施用量达到600 kg.hm-2时,土壤pH值显著高于对照,土壤有效态镉质量分数较对照降低10.9%（P〈0.05）,水稻茎叶和糙米中镉质量分数分别降低36.8%（P〈0.05）和33.0%（P〈0.05）。等量条件下（600 kg.hm-2）石灰氮对降低土壤镉有效性及水稻累积镉的效果相对优于石灰处理。因此,石灰氮与石灰一样可用于酸性重金属污染土壤的修复与改良,是一种极具潜力的土壤改良剂。     

镉污染土壤对潜在能源植物生长的影响

利用重金属污染土壤种植能源植物是一种同时解决环境问题和能源问题的新理念,但目前相关研究成果并不多。通过盆栽试验研究人工镉污染土壤中象草Pennisetumpurpureum和亚香茅Cymbopogonnardus两种植物植株的生长状况和两种植物对土壤镉的吸收和富集能力。结果表明,当外源可溶性镉加入到土壤后,其主要是以生物有效性较高的状态存在。土壤镉对象草和亚香茅生长的影响作用有很大的不同,亚香茅比象草具有更强的镉耐受力,其生物量受镉污染影响小。两种植物植株镉含量均随土壤镉添加量的增加而增加。除高镉处理象草外,植物地下部分含镉量比地上部分高很多。高镉处理象草地下部分含镉量比地上部分低的现象可能反映出根系已积累了太多的镉,因而加速了向地上部的转移,从而加剧了植物中毒的程度。赤泥添加剂具有降低土壤酸度,减少植物对镉的吸收和增加象草和亚香茅生物量的作用。     

Cadmium distribution in rice plants grown in three different soils after application of pig manure with added cadmium

A glasshouse pot experiment was conducted to investigate Cd concentrations in the aboveground parts of two consecutive crops of rice and Cd availability in three different soils (loam, silt loam, and sandy loam) after application of pig manure with added Cd. Soil pH tended to increase with increasing application rate of pig manure from 1 to 3% (w/w, oven dry basis). Soil diethylene triamine pentaacetic acid (DTPA) extractable Cd showed a clear positive correlation with soil total Cd content and increased with increasing Cd amendment of the manure but showed no difference between the two manure application rates. Cd concentrations in the grain, husk, and straw were significantly and positively correlated with soil DTPA-extractable Cd (p < 0.001). Within each level of manure Cd, the higher rate (3%) of manure produced lower Cd concentrations in the grain, husk, and straw on all three soils than did the lower rate (1%) after the first crop, but this no longer occurred after the growth of the second crop. Grain Cd concentrations exceeded the Chinese National Food Quality Standard (0.2 mg kg(-1)) most often on the loam, with intermediate frequency on the silt loam, and least often on the sandy loam, the soil with the highest pH and lowest organic carbon content and cation exchange capacity.     

Metabolic responses of Azolla pinnata to cadmium stress: photosynthesis,antioxidative system and phytoremediation

This present study deals with the growth, photosynthesis, oxidative stress and phytoremediation character of Azolla pinnata L. exposed to different levels (0.05, 0.1, 0.5, 1.0, 1.5 and 2.0 mg·L^?1) of cadmium (Cd). Significant accumulation of Cd in Azolla fronds was noticed after 24 and 96 h of exposure and the accumulation rate was dose and time dependent. Growth of A. pinnata increased significantly after both exposure times with and without metal. At lower Cd doses (0.05 and 0.1 mg·L^?1), growth and photosynthesis of A. pinnata showed a marginal increase over the respective control, however, at higher Cd doses (0.5, 1.0, 1.5 and 2.0 mg·L^?1), a decreasing trend was noticed. At lower doses, Azolla fronds could counterbalance the negative effect of enhanced levels of superoxide radicals (SOR) and hydrogen peroxide (H₂O₂) through the greater activity of antioxidative enzymes. The decaresing trends in catalase and peroxidase activity at higher Cd doses suggest that Azolla fronds were not able to mitigate the negative effects of H₂O₂, hence an increase in malondialdehyde content was noticed. The study concludes that up to 0.1 ,mg·L^?1 Cd, A. pinnata can flourish and be used as biofertiliser and for phytoremedial purposes in Cd-contaminated fields; beyond this concentration poor growth may restrict its application.     

Impact of cadmium and lead on Catharanthus roseus--a phytoremediation study

The Madagascar Periwinkle, Catharanthus roseus (L.) G. Don (a valued medicinal plant) was exposed to different concentrations ofheavymetals like, CdCl, and PbCl, with a view to observe their bioaccumulation efficiency. Germination was inhibited by both the heavy metals in the seeds previously imbibed in GA, and KNO, for 24 hr. EC50 (the effective concentration which inhibits root length by 50%) was recorded as 180 microM for CdCl2, and 50 microM for PbCl2. Both alpha-amylase and protease activity were reduced substantially on treatment of seeds with increasing concentrations of CdCl2, and PbCl2. Malondialdehyde (MDA) a product of lipoxigenase (LOX) activity also increased due to the treatment of both CdCl, and PbCl2. When two-months-old plants grown in normal soil were transferred to soils containing increasing amounts of these two heavy metals, senescence of lower leaves and extensive chlorosis were noticed after four days of transfer However, plants gradually acclimatized and after 20 days the chlorophyll content was almost comparable to normal. Plants receiving CdCl2 treatment (250 microg g(-1) and less) became acclimatized after two weeks and started normal growth. But PbCl2 of 432 microg g(-1) and less could not affect the plant growth throughout, after a preliminary shock was erased. In case of CdCl2 treatment, a stunted growth with reduced leaf area, reduced biomass and sterility were recorded after six months, while plants show normal growth and flowering in case of PbCl2 treatment. Total alkaloid was also found to be decreased in the roots of CdCl2 treated plants. No change was observed in case of PbCl2. GA3 treatments to the CdCl2 treated plants show internode elongation and increase in leaf area with relatively elongated leaves and thinning of stem diameter AAS analyses of leaves of treated plants exhibited 5-10% accumulation of cadmium, but there was no accumulation of lead at all.     

Effect of arbuscular mycorrhizal (AM) fungus and plant growth promoting rhizomicroorganisms (PGPR's) on medicinal plant Solanum viarum seedlings

A green house nursery study was conducted to assess the interaction between arbuscular mycorrhizal (AM) fungus, Glomus aggregatum and some plant growth promoting rhizomicrooganisms (PGPR's), Bacillus coagulans and Trichoderma harzianum, in soil and their consequent effect on growth, nutrition and content of secondary metabolities of Solanum viarum seedlings. Triple inoculation of G. aggregatum+B. coagulans+T. harzainum with Solanum viarum in a green house nursery study resulted in maximum plant biomass (plant height 105 cm and plant dry weight 12.17 g), P, Fe, Zn, Cu and Mn and secondary metabolities [total phenols (129.6 microg g(-1) f.wt.), orthodihydroxy phenols (90.6 microg g(-1) f.wt.), flavonoids (3.94 microg g(-1) f.wt.), alkaloids (5.05 microg g(-1) f.wt.), saponins (5.05 microg g(-1) f.wt.) and tannins (0.324 microg g(-1) f.wt.)] of S. viarum seedlings. The mycorrhizal root colonization and spore numbers in the root zone soil of the inoculated plants increased. The enzyme activity namely acid phosphatase (53.44 microg PNP g(-1) soil), alkaline phosphatase (40.95 microg PNP g(-1) soil) and dehydrogenase (475.5 microg PNP g(-1) soil) and total population of B. coagulans (12.5x10(4) g(-1)) and T. harzianum (12.4 x 10(4) g(-1)), in the root zone soil was found high in the triple inoculation with G. aggregatum+B. coagulans+T. harzianum that proved to be the best microbial consortium.     

Uptake of zinc, cadmium and phosphorus by arbuscular mycorrhizal maize (Zea mays L.) from a low available phosphorus calcareous soil spiked with zinc and cadmium

In a multifactorial pot experiment, maize (Zea mays L.) with or without inoculation with the arbuscular mycorrhizal (AM) fungus Glomus mosseae BEG167 was grown in a sterilized soil spiked with three levels of zinc (0, 300 and 900 mg Zn kg⁻¹ soil) and three levels of cadmium (0, 25 and 100 mg Cd kg⁻¹ soil). At harvest after 8 weeks of growth, the proportion of root length of inoculated plants colonized decreased with increasing Zn or Cd additon, and was 56% in the absence of both metals and was reduced significantly to 27% in the presence of the higher levels of both metals. Mycorrhizal plants had higher biomass than non-mycorrhizal controls except at the highest soil level of Cd. Cadmium had more pronounced effects on plant biomass than did Zn at the levels studied and the two metals showed a significant interaction. The data suggest that mycorrhizal inoculation increased plant growth with enchancement of P nutrition, perhaps increasing plant tolerance to Zn and Cd by a dilution effect. AM inoculation also led to higher soil solution pH after harvest, possibly reducing the availability of the metals for plant uptake, and lowered the concentrations of soluble Zn and Cd in the soil solution, perhaps by adsorption onto the extrametrical mycelium.     

4种改良剂对土壤-黑麦草系统中镉行为的影响

以黑麦草（Lolium perenne L.）作为修复植物,开展了石灰、磷灰石、木炭、猪粪4种改良剂对重金属Cd污染土壤的田间原位修复试验研究。结果表明：改良剂提高了土壤pH值并促进土壤Cd从生物可利用性高的形态向迟效态转化,降低对生物和环境的直接毒害作用,促进黑麦草的生长。以黑麦草生物量和Cd富集量的增加作为评价指标,4种改良剂修复Cd污染土壤效果依次为：石灰〉磷灰石〉木炭〉猪粪。石灰处理中黑麦草Cd富集量为13.11 mg,与其他处理均呈现显著差异。污染土壤重金属Cd的化学形态与黑麦草对Cd的吸收密切相关。黑麦草地上部分Cd质量分数,与土壤B-2态Cd呈极显著正相关关系,相关系数为0.730。黑麦草地下部分Cd质量分数,与B-2、B-3态Cd均呈极显著正相关关系,相关系数分别为0.756、0.786;黑麦草地上部分和地下部分Cd质量分数均与B-4态Cd呈极显著负相关关系,相关系数分别为0.757和0.708。     

镉对桑蚕生长发育和蚕茧质量影响的研究

研究了土壤镉对桑叶含镉量［w（Cd）］、含水量［w（H2O）］的影响以及镉对蚕生长发育和蚕茧质量的影响结果表明：（1）桑叶w（Cd）与土壤w（Cd）呈极显著正相关（2）土壤w（Cd）＞22．3×10-6,则桑叶w（H20）＜75％,叶质开始变粗硬,（3）用w（Cd）＜3．66×10-6的添加Cd桑叶养蚕时,蚕能正常生长发育,蚕茧质量不受影响（4）当镉由土壤进入桑叶,用w（Cd）＜0．49×10-6的桑叶养蚕时,蚕的生长发育和蚕茧质量不受明显影响（5）当桑叶w（Cd）超过上述数值后,蚕的生长发育受阻,蚕茧质量明显下降。     

天然沸石对土壤镉及番茄生物量的影响

为了探索沸石对轻度镉污染土壤的修复效果及对番茄生长的影响,利用盆栽试验研究了不同沸石添加量及不同沸石粒级等因素对不同生长时期番茄（Solanum lycopersicum）植株生物量、果实产量和土壤镉质量分数的影响。结果表明,添加沸石均不同程度地提高不同生长期番茄地上部生物量和果实产量;每千克土壤添加10 g的大粒级（MX）沸石使得土壤全镉和有效镉增加最多,同时也使番茄果实增产最多,每千克土壤添加18 g的小粒级（MN）沸石使得土壤全镉质量分数有所降低,土壤有效镉质量分数增加最少,同时也可使番茄果实增产42.9%以上。小粒级（MN）沸石为削减土壤重金属镉的最佳沸石粒级,18 g.kg-1为削减土壤重金属镉的最佳沸石添加量。     

Pollution of River Mahaweli and farmlands under irrigation by cadmium from agricultural inputs leading to a chronic renal failure epidemic among farmers in NCP, Sri Lanka

Chronic renal failure (CRF) associated with elevated dietary cadmium (Cd) among farming communities in the irrigated agricultural area under the River Mahaweli diversion scheme has reached a significantly higher level of 9,000 patients. Cadmium, derived from contaminated phosphate fertilizer, in irrigation water finds its way into reservoirs, and finally to food, causing chronic renal failure among consumers. Water samples of River Mahaweli and its tributaries in the upper catchment were analyzed to assess the total cadmium contamination of river water and the possible source of cadmium. Except a single tributary (Ulapane Stream, 3.9?μg?Cd/l), all other tested tributaries carried more than 5?μg?Cd/l, the maximum concentration level accepted to be safe in drinking water. Seven medium-sized streams carrying surface runoff from tea estates had 5.1-10?μg?Cd/l. Twenty larger tributaries (Oya), where the catchment is under vegetable and home garden cultivation, carried 10.1-15?μg?Cd/l. Nine other major tributaries had extremely high levels of Cd, reaching 20?μg?Cd/l. Using geographic information system (GIS), the area in the catchment of each tributary was studied. The specific cropping system in each watershed was determined. The total cadmium loading from each crop area was estimated using the rates and types of phosphate fertilizer used by the respective farmers and the amount of cadmium contained in each type of fertilizer used. Eppawala rock phosphate (ERP), which is mostly used in tea estates, caused least pollution. The amount of cadmium in tributaries had a significant positive correlation with the cadmium loading of the cropping system. Dimbula Tea Estate Stream had the lowest Cd loading (495.9?g/ha/year), compared with vegetable-growing areas in Uma Oya catchment with 50,852.5?g?Cd/ha/year. Kendall's τ rank correlation value of total Cd loading from the catchment by phosphate fertilizer used in all crops in the catchment to the Cd content in the tributaries was +0.48. This indicated a major contribution by the cropping system in the upper catchment area of River Mahaweli to the eventual Cd pollution of river water. Low soil pH (4.5-5.2), higher organic matter content (2-3%), and 18-20?cmol/kg cation exchange capacity (CEC) in upcountry soil have a cumulative effect in the easy release of Cd from soil with the heavy surface runoff in the upcountry wet zone. In view of the existing water conveyance system from upcountry to reservoirs in North Central Province (NCP) through diversion of River Mahaweli, in addition to their own nonpoint pollution by triple superphosphate fertilizer (TSP), this demands a change in overall upper catchment management to minimize Cd pollution through agriculture inputs to prevent CRF due to elevated dietary cadmium among NCP farmers.     

Effects of cadmium on nutrient uptake and translocation by Indian Mustard

Plants that hyperaccumulate metals are ideal subjects for studying the mechanisms of metal and mineral nutrient uptake in the plant kingdom. Indian Mustard (Brassica juncea) has been shown to accumulate moderate levels of Cd, Pb, Cr, Ni, Zn, and Cu. In this experiment, 10 levels of Cd concentration treatments were imposed by adding 10-190 mg Cd kg(-1) to the soils as cadmium nitrate [Cd(NO3)2]. The effect of Cd on phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and the micronutrients iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in B. juncea was studied. Plant growth was affected negatively by Cd, root biomass decreased significantly at 170 mg Cd kg(-1) dry weight soils treatment. Cadmium accumulation both in shoots and roots increased with increasing soil Cd treatments. The highest concentration of Cd was up to 300 mg kg(-1) d.w. in the roots and 160 mg kg(-1) d.w. in the shoots. The nutrients mainly affected by Cd were P, K, Ca, Fe, and Zn in the roots, and P, K, Ca, and Cu in the shoots. K and P concentrations in roots increased significantly when Cd was added at 170 mg kg(-1), and this was almost the same level at which root growth was inhibited. Zn concentrations in roots decreased significantly when added Cd concentration was increased from 50 to 110 mg kg(-1), then remained constant with Cd treatments from 110 to 190 mg kg(-1). However, Zn concentrations in the shoots seemed less affected by Cd. It is possible that Zn uptake was affected by the Cd but not the translocation of Zn within the plant. Ca and Mg accumulation in roots and shoots showed similar trends. This result indicates that Ca and Mg uptake is a non-specific process.     

Biosolids application affects the competitive sorption and lability of cadmium,copper, nickel,lead, and zinc in fluvial and calcareous soils

The objective of this research was to investigate the effects of biosolids on the competitive sorption and lability of the sorbed Cd, Cu, Ni, Pb, and Zn in fluvial and calcareous soils. Competitive sorption isotherms were developed, and the lability of these metals was estimated by DTPA extraction following their sorption. Sorption of all metals was higher in the fluvial than in the calcareous soil. Sorption of Cu and Pb was stronger than that of Cd, Ni, and Zn in all soils. Biosolids application (2.5%) reduced the sorption of all metals especially Cu and Pb (28–43%) in both soils (especially the calcareous soil) at the lower added metal concentrations (50 and 100 mg L^?1). However, it increased the sorption of all metals especially Pb and Cu in both soils (especially the calcareous soil; 15.5-fold for Cu) at the higher added concentrations (250 and 300 mg L^?1). Nickel showed the highest lability followed by Cd, Zn, and Pb in both soils. Biosolids increased the lability of the sorbed Ni in the fluvial soils at all added concentrations and the lability of Cd, Pb, and Zn at 50 mg L^?1, but decreased the lability of Cd, Pb, and Zn at 250 and 300 mg L^?1 in both soils. We conclude that at low loading rate (e.g., 50 mg L^?1) biosolids treatment might increase the lability and environmental risk of Cd, Cu, Pb, and Zn. However, at high loading rate (e.g., 300 mg L^?1) biosolids may be used as an immobilizing agent for Cd, Cu, Pb, Zn and mobilizing agent for Ni.     

The Environmental Capacity Approach to the Control of Marine Pollution: The Case of Copper in the Krka River Estuary

Changes in soil pH, soil heavy metal forms, and the metabolic diversity of microbial communities were examined in soil samples collected in 1-mm increments from barley roots in soil contaminated with cadmium (Cd) and zinc (Zn) using a rhizobox system. Concentrations of exchangeable Cd and Zn increased near the roots owing to a decrease in soil pH. Conversely, the concentration of inorganically bound Cd and Zn decreased near the roots. Despite having the highest concentration of the most toxic exchangeable metals, the rhizosphere also had the highest bacterial and fungal metabolic activity and diversity when assessed using BIOLOG plates. Therefore, the promoting effects of root exudates on microbial activity could outweigh the adverse effects of Cd and Zn on microorganisms in the rhizosphere.     

Effect of phosphogypsum amendment on soil physico-chemical properties, microbial load and enzyme activities

Phosphogypsum (PG) is produced as a solid waste from phosphatic fertilizer plants. The waste slurry is disposed off in settling ponds or in heaps. This solid waste is now increasingly being used as a calcium supplement in agriculture. This study reports the effectof PG amendmenton soil physico chemical properties, bacterial and fungal count and activities of soil enzymes such as invertase, cellulase and amylase over an incubation period of 28 days. The highest mean percent carbon loss (55.98%) was recorded in 15% PG amended soil followed by (55.28%) in 10% PG amended soil and the minimum (1.68%) in control soil. The highest number of bacterial colonies (47.4 CFU g(-1) soil), fungal count (17.8 CFU g(-1) soil), highest amylase activity (38.4 microg g(-1) soil hr(-1)) and cellulase activity (38.37 microg g(-1) soil hr(-1)) were recorded in 10% amended soil. Statistically significant difference (p<0.05) has been recorded in the activities of amylase and cellulase over the period of incubation irrespective of amendments. Considering the bacterial and fungal growth and the activities of the three soil enzymes in the control and amended sets, it appears that 10% PG amendment is optimal for microbial growth and soil enzyme activities.     

Antioxidative response of Lemna polyrrhiza L. to cadmium stress

Growth, lipid peroxidation, different antioxidative enzymes and metal accumulation were studied in Lemna polyrrhiza treated with different concentrations (1-40 ppm) of CdSO4. The growth of the plant was slightly enhanced with 1 ppm, while higher concentrations retarted growth and multiplication of fronds, the effect being concentration and dose dependant. Increase in malondialdehyde content was insignificant after the first week but a prolonged exposure led to significant (p < 0.05) increase of about 38% and 45% over the control in 20 and 30 ppm, respectively after four weeks. Catalase (EC 1.11.1.6; CAT) activity increased at low concentration, but it declined to 42% and 54% at 40 ppm after 6 and 30 days, respectively Superoxide dismutase (EC 1.15.1.1; SOD), ascorbate peroxidase (EC 1.11.1.11;APx) and glutathione reductase (EC 1.6.4.2) increased at both low as well at high concentrations, but a prolonged exposure to high concentration of Cd (40 ppm) led to significant (p < 0.05) decline in the mean activities of these antioxidant enzymes. Accumulation of Cd in biomass was concentration and time dependant However at high concentration of 40 ppm, Cd accumulation did not increase significantly (p < 0.05) with time. Increased activities of antioxidant enzymes in Cd treated plants suggest that metal tolerance in L. polyrrhiza might be associated to the changes of antioxidant enzymatic activities.