Lead induced responses of Pfaffia glomerata, an economically important Brazilian medicinal plant, under in vitro culture conditions.

Plantlets of Pfaffia glomerata (Spreng.) were exposed in vitro for 30 days to five lead levels (0-400 µM) to analyze the effects on growth and oxidative stress and responses of various antioxidants vis-à-vis lead accumulation. The plantlets showed significant lead accumulation in roots (1,532 µg g(-1) DW) with a low root to shoot lead translocation (ca. 3.6%). The growth of plantlets was negatively affected by various lead treatments, although the level of photosynthetic pigments did not alter significantly in response to any lead treatment. However, plantlets suffered from oxidative stress as suggested by the significant increase in malondialdehyde levels in root (8.48 µmol g(-1) FW) and shoot (3.20 µmol g(-1) FW) tissues with increasing lead treatments. In response to the imposed toxicity, increases in the activities of catalase in root (4.14 ∆E min(-1) mg(-1) protein) and shoot (3.46 ∆E min(-1) mg(-1) protein) and superoxide dismutase in root (345.32 units mg(-1) protein) and shoot (75.26 units mg(-1) protein), respectively, were observed, while the levels of non-protein thiols and ascorbic acid were not affected significantly in either roots or shoots.

Adsorption-desorption characteristics of mercury in paddy soils of China.

Mercury (Hg) has received considerable attention because of its association with various human health problems. Adsorption-desorption behavior of Hg at contaminated levels in two paddy soils was investigated. The two representative soils for rice production in China, locally referred to as a yellowish red soil (YRS) and silty loam soil (SLS) and classified as Gleyi-Stagnic Anthrosols in FAO/UNESCO nomenclature, were respectively collected from Jiaxin County and Xiasha District of Hangzhou City, Zhejiang Province. The YRS adsorbed more Hg(2+) than the SLS. The characteristics of Hg adsorption could be described by the simple Langmuir adsorption equation (r2 = 0.999 and 0.999, P < 0.01, respectively, for the SLS and YRS). The maximum adsorption values (Xm) that were obtained from the simple Langmuir model were 111 and 213 mg Hg(2+) kg(-1) soil, respectively, for the SLS and YRS. Adsorption of Hg(2+) decreased soil pH by 0.75 unit for the SLS soil and 0.91 unit for the YRS soil at the highest loading. The distribution coefficient (kd) of Hg in the soil decreased exponentially with increasing Hg(2+) loading. After five successive desorptions with 0.01 mol L(-1) KCl solution (pH 5.4), 0 to 24.4% of the total adsorbed Hg(2+) in the SLS soil was desorbed and the corresponding value of the YRS soil was 0 to 14.4%, indicating that the SLS soil had a lower affinity for Hg(2+) than the YRS soil at the same Hg(2+) loading. Different mechanisms are likely involved in Hg(2+) adsorption-desorption at different levels of Hg(2+) loading and between the two soils.

Arsenic accumulation in root and shoot vis-a-vis its effects on growth and level of phytochelatins in seedlings of Cicer arietinum L.

Arsenic (As) contamination of water and soil has become a subject of prime interest due to its direct effect on human health through drinking water and food. In present study two varieties (CSG-8962 and C-235) of chickpea, Cicer arietinum L., which is a major supplementary food in many parts of India and a valuable source of protein, has been selected to estimate the level of arsenate in root and shoot of five day old seedlings vis-à-vis effect of arsenate on seedling growth and induction of thiols including glutathione (GSH) and phytochelatins (PCs) and their homologues. Both varieties accumulated arsenate to similar levels and most of the metalloid was confined to roots, only about 2.5% was translocated to shoot. Plant growth was also not affected significantly in both the varieties. Arsenate exposure significantly induced the levels of thiols including PCs and homophytochelatins (hPCs). The induction of thiols was much higher in roots than shoots and was greater in var C-235 between the two tested ones. Thus, both varieties tolerated and detoxified arsenic through chelation with GSH, PCs and hPCs, primarily in roots, however var C-235 performed better

Correlation analysis of mineral element contents and quality traits in milled rice (Oryza stavia L.).

The relationships among potassium (K), calcium (Ca), sodium (Na), magnesium (Mg), iron (Fe), zinc (Zn), copper (Cu), and manganese (Mn) contents in milled rice (Oryza stavia L.) of 274 genotypes and the relationships between these mineral element contents and other rice quality traits including 3 cooking quality traits, 17 amino acid contents, and protein content were investigated. The results showed that there were significant correlations among most of mineral element contents. Mg, Fe, and Mn contents were significantly correlated with most of the other mineral element contents, while Cu content had significantly negative associations with the K and Mg contents of rice. The relationships between mineral element contents and cooking quality traits showed that gel consistency (GC) was significantly correlated with K, Cu, and Mn contents of rice. Amylose content (AC) was significantly associated with K, Na, Mg, Cu, and Mn contents. The alkali spreading value (ASV) had closely positive relationships with Ca, Mg, and Mn contents. In addition, 8 mineral element contents had obvious correlations with different amino acid contents. Mg, Ca, and Zn contents were significantly correlated with most of the 17 amino acid contents, but Na content did not correlate with amino acid contents except aspartic acid of rice. Furthermore, significant associations were found between protein content and Na, Mg, Zn, Cu, or Mn content. Six principal components were extracted to explain 84.50% of the total variances and contained the information provided by the original 29 variables according to the principal component analysis.

Effects of pH, organic acids, and competitive cations on mercury desorption in soils.

The effects of pH, organic acids, and competitive cations on Hg(2+) desorption were studied. Three representative soils for rice production in China, locally referred to as a yellowish red soil (YRS), purplish clayey soil (PCS), and silty loam soil (SLS) and classified as Gleyi-Stagnic Anthrosols in FAO/UNESCO nomenclature, were, respectively, collected from Jiaxin County, Deqing County, and Xiasha District of Hangzhou City, Zhejiang Province. Most of the added Hg(2+) was adsorbed at low initial concentrations (<2 mg l(-1)). Desorption of the adsorbed Hg(2+) in 0.01M KCl (simulating soil solution) was minimal, but was significantly enhanced by the change of pH, and the presence of organic acids or competitive cations. The desorption of Hg(2+) in the soils decreased with pH from 3.0 to 5.0, leveled off at pH 5.0-8.0, but increased with pH from 7.0 to 9.0. The presence of organic ligands enhanced Hg(2+) desorption in the soils except for YRS, in which the addition of tartaric, malic, or oxalic acid reduced Hg(2+) desorption at low concentrations (<10(-4)M), but Hg(2+) desorption generally increased with organic acid concentration. Citric acid was most effective in increasing Hg(2+) desorption, followed by tartaric acid and malic acid; and oxalic acid was the least effective. Desorption of adsorbed Hg(2+) increased with increasing concentrations of added Cu(2+) or Zn(2+). Applied Cu(2+) increased Hg(2+) desorption more than Zn(2+) at the same loading rate. CAPSULE: The effects of organic acids and competitive cations on Hg desorption in soil-water system are related to their concentrations, basic chemical properties, and soil properties.

Leaching potential of heavy metals (Cd, Ni, Pb, Cu and Zn) from acidic sandy soil amended with dolomite phosphate rock (DPR) fertilizers.

There is an increasing concern on heavy metal leaching from the soils amended with sewage sludge. A column study was conducted to examine the extent of leaching of five important heavy metals (Cd, Ni, Pb, Cu and Zn) from an acidic sandy soil amended with different dolomite phosphate rock (DPR) fertilizers (an application rate of 1% fertilizers) developed from DPR and N-Viro (consisting of biosolids and fly ash) at 0%, 10%, 20%, 30%, 40%, 50% and 100% DPR. Ten leaching events were carried out with each event done at an interval of 7 days and with total leaching volume of 1183mm, which is equivalent to the mean annual rainfall of this region during the period of 2001-2003. Leachate was collected after each leaching event and analyzed for heavy metals. The maximum leachate concentrations of Cd, Ni, Pb, Cu and Zn were all below drinking water quality guidance limits set by Florida Department of Environmental Protection and World Health Organization, suggesting that the application of DPR fertilizers may not pose a threat to water quality by leaching. Most of leachate concentrations of Cd, Ni and Pb were below their detection limits and there were no significant differences between the control and the treatments with different DPR fertilizers. By contrast, there were higher leachate concentrations of Cu and Zn (ranging from 0.7 to 37.1mug Cu/l and 5.1 to 205.6mug Zn/l for all treatments) due to their higher contents in both the soil and different DPR fertilizers compared with Cd, Ni and Pb. The leachate concentrations of Cu and Zn for each treatment decreased with increasing leaching events. The differences in leachate concentrations of Cu and Zn between the control and the treatments with different DPR fertilizers containing N-Viro were significant, especially in the first several leaching events and, moreover, they increased with increasing proportion of N-Viro in the DPR fertilizers. There were similar trends in total losses of Cu and Zn after ten leaching events. Greater differences in both leachate concentrations and total losses of Zn between the control and the treatments containing N-Viro were noted. Total losses of Zn for the treatments containing N-Viro were 3.0-5.1 times higher than those for the control compared with 1.4-2.2 times higher for total losses of Cu, suggesting that greater proportions of Zn losses came from the DPR fertilizers due to the greater mobility of Zn in the DPR fertilizers compared with Cu.

Use of dolomite phosphate rock (DPR) fertilizers to reduce phosphorus leaching from sandy soil.

There is increasing concern over P leaching from sandy soils applied with water-soluble P fertilizers. Laboratory column leaching experiments were conducted to evaluate P leaching from a typical acidic sandy soil in Florida amended with DPR fertilizers developed from dolomite phosphate rock (DPR) and N-Viro soil. Ten leaching events were carried out at an interval of 7 days, with a total leaching volume of 1,183 mm equivalent to the mean annual rainfall of this region during the period of 2001-2003. Leachates were collected and analyzed for total P and inorganic P. Phosphorus in the leachate was dominantly reactive, accounting for 67.7-99.9% of total P leached. Phosphorus leaching loss mainly occurred in the first three leaching events, accounting for 62.0-98.8% of the total P leached over the whole period. The percentage of P leached (in the total P added) from the soil amended with water-soluble P fertilizer was higher than those receiving the DPR fertilizers. The former was up to 96.6%, whereas the latter ranged from 0.3% to 3.8%. These results indicate that the use of N-Viro-based DPR fertilizers can reduce P leaching from sandy soils.

Effects of pH, organic acids, and inorganic ions on lead desorption from soils.

The desorption characteristics of lead in two variable charge soils (one developed from Arenaceous rock (RAR) and the other derived from Quaternary red earths (REQ)) were studied, and the effects of pH value, organic acid, and competitive ions were examined. Desorption of Pb(2+) decreased from nearly 100.0 to 20.0% within pH 1.0-4.0 in both soils, and then the decrease diminished at pH > 4.0. Organic ligands at relatively low concentrations (< or =10(-3) mol L(-1)) slightly inhibited Pb(2+) desorption, but enhanced Pb(2+) desorption at higher concentrations. In this study, citric acid or acetic acid at higher concentrations (>10(-3) mol L(-1)) had the greatest improvement of Pb(2+) desorption, followed by malic acid; and the smallest was oxalic acid. Desorption of the adsorbed Pb(2+) increased greatly with increasing concentrations of added Cu(2+) or Zn(2+). Applied Cu(2+) increased Pb(2+) desorption more than Zn(2+) at the same loading.

Growth response and phytoextraction of copper at different levels in soils by Elsholtzia splendens.

Phytoremediation is a promising approach for cleaning up soils contaminated with heavy metals. Information is needed to understand growth response and uptake mechanisms of heavy metals by some plant species with exceptional capability in absorbing and superaccumulating metals from soils. Greenhouse study, field trial, and old mined area survey were conducted to evaluate growth response and Cu phytoextraction of Elsholtzia splendens in contaminated soils, which has been recently identified to be tolerant to high Cu concentration and have great potential in remediating contaminated soils. The results from this study indicate that the plant exhibited high tolerance to Cu toxicity in the soils, and normal growth was attained up to 80 mg kg(-1) available soil Cu (the NH4OAc extractable Cu) or 1000 mg kg(-1) total Cu. Under the field conditions, a biomass yield of 9 ton ha(-1) was recorded at the soil available Cu level of 77 mg kg(-1), as estimated by the NH4OAc extraction method. Concentration-dependent uptake of Cu by the plant occurred mainly at the early growth stage, and at the late stage, there is no difference in shoot Cu concentrations grown at different extractable soil Cu levels. The extractability of Cu from the highly polluted soil is much greater by the roots than that by the shoots. The NH4OAc extractable Cu level in the polluted soil was reduced from 78 to 55 mg kg(-1) in the soil after phytoextraction and removal of Cu by the plant species for one growth season. The depletion of extractable Cu level in the rhizosphere was noted grown in the mined area, even at high Cu levels, the NH4OAc extractable Cu in the rhizosphere was 30% lower than that in the bulk soil. These results indicate that phytoextraction of E. splendens can effectively reduce the plant-available Cu level in the polluted soils.

Solubility of phosphorus and heavy metals in potting media amended with yard waste-biosolids compost.

The potential risk of surface and ground water contamination by phosphorus (P) and heavy metals leached from compost-based containerized media has become an environmental concern. Solubility and fractionation of P and heavy metals were evaluated in media containing 0, 25, 50, 75, or 100% compost derived from biosolids and yard trimmings for potential impacts on the environment. As compost proportion in peat-based media increased from 0 to 100%, concentrations of total P, Cd, Cu, Ni, Pb, Zn, and Mn in the media increased whereas concentrations of total Co and Cr decreased. Except for Cu, all heavy metals in the water-soluble fraction decreased with increasing compost proportion in the media, because of higher Fe, Al, and Ca concentrations and pH values of the composts than the peat. When the media pH is controlled and maintained at normal range of plant growth (5.5-6.5), leaching of the heavy metals is minimal. Incorporation of compost to the peat-based media also decreased the proportion of total P that was water-soluble. However, concentrations of bioavailable inorganic phosphorus (NaHCO3-IP), readily mineralizable organic phosphorus (NaHCO3-OP), potentially bioavailable inorganic phosphorus (NaOH-IP), and potentially bioavailable organic phosphorus (NaOH-OP) were still higher in the media amended with compost because of higher total P concentration in the compost. Further study is needed to verify if less or no topdressing of chemical P fertilizer should be applied to the compost-amended media to minimize P effect on the environment when compost-amended potting media are used for nursery or greenhouse crop production systems.

[Heart morphologic state in retired fighter pilots].

Objective. To study the heart morphology in the retired fighter pilots, and to provide clinical evidence for protection combined G-loads (+ Gz), heat, noise, hypoxic and vibration stress induced cardiac structural damage. Method. Parameters of heart morphology were studied using Doppler echocardiography in 40 retired fighter pilots with 40 veteran cadres as control. Result. LVDd, LVDs, LADs, LVEDV, LVPWs and LVM in pilot group were somewhat higher than those in control group (NS); while IVSs and LVMI in pilot group were slightly lower than those in control group (NS); LVESV, aortic valve area, internal diameter of the ring and sinus in pilot group were significantly higher than those in control group (P < 0.05). Conclusion. Analysis of the results revealed no pathomorphologic damage of the heart. It suggest that all the variations can be regarded as adaptive changes due to the effects of the combined environmental factors experienced in long time flying.

The detoxification of lead in Sedum alfredii H. is not related to phytochelatins but the glutathione.

Two ecotypes of S. alfredii [Pb accumulating (AE) and Pb non-accumulating (NAE)] differing in their ability in accumulating Pb were exposed to different Pb levels to evaluate the effects on plant length, photosynthetic pigments, antioxidant enzymes (SOD and APX), cysteine, non-protein thiols (NP-SH), phytochelatins (PCs) and glutathione (GSH) vis-à-vis Pb accumulation. Both ecotypes showed significant Pb accumulation in roots, however only the AE showed significant Pb accumulation in shoots. We found that both AE and NAE of S. alfredii-induced biosynthesis of GSH rather than phytochelatins in their tissue upon addition of even high Pb levels (200 microM). Root and shoot length were mostly affected in both ecotypes after addition of higher Pb concentrations and on longer durations, however photosynthetic pigments did not alter upon addition of any Pb treatment. Both superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities of AE were higher than NAE. The levels of cysteine and NP-SH were also higher in AE than in NAE. Hence, the characteristic Pb accumulation of ecotypes differed presumably in relation to their capacity for detoxification of Pb. These results suggest that enzymatic and non-enzymatic antioxidants play a key role in the detoxification of Pb-induced toxic effects in Sedum alfredii. This plant can be used as an indicator species for Pb contamination.

Effect of long-term stress of high Pb/Zn levels on genomic variation of Sedum alfredii Hance.

In this study, the heavy metal contents were detected in plants of Sedum alfredii and soils from Pb/Zn mined area and non-mined area, and a dendrogram was generated by using RAPD methods based on the hyperaccumulating ecotype (HE), the non-hyperaccumulating ecotype (NHE) and other species of Sedum. The results showed that the available Pb of the Pb/Zn mined soil was 77-fold higher, and available Zn and Cd were 10-fold and 16-fold higher in the mined soil than in the non-mined soil, respectively. The dendrogram showed that the HE S. alfredii was the nearest relative to NHE S. alfredii. However, genomic variation of two ecotypes was still notable, indicating that heavy metal stress had great impacts on the genetic diversity and plant evolution, and HE may be a mutant from the NHE. Ten RAPD bands were observed only in the HE as compared with other species of Sedum. The character of Zn/Cd hyperaccumulation in HE appeared to be related to SH-containing compounds and resist osmotic stress, and also many unknown genes.

Assessing lead thresholds for phytotoxicity and potential dietary toxicity in selected vegetable crops.

Lead tolerance and accumulation in shoots and edible parts varied with crop species and soil type. The critical Pb concentrations at 10% yield reduction were 24.71, 28.25, and 0.567 mg kg(-1) for pakchoi, celery, and hot pepper, respectively under hydroponic conditions, whereas were 13.1, 3.83, 0.734 mg kg(-1) grown in the Inceptisol and 31.7, 30.0, 0.854 mg kg(-1) in the Alluvial soil, respectively. Based on the threshold of human dietary toxicity for Pb, the critical levels of soil available Pb for pakchoi, celery, and hot pepper were 5.07, 8.06, and 0.48 mg kg(-1) for the Inceptisol, and 1.38, 1.47, and 0.162 mg kg(-1) for the Alluvial soil, respectively. Similarly, the total soil Pb thresholds were different from vegetable species and soil types.

Effects of repeated applications of chlorpyrifos on its persistence and soil microbial functional diversity and development of its degradation capability.

Effects of repeated applications of chlorpyrifos on its persistence and soil microbial functional diversity were studied under laboratory conditions. The results showed that the degradation rate of chlorpyrifos increased whereas its inhibitory effect on soil microbial communities gradually decreased with application frequency of chlorpyrifos. A bacterial strain DSP capable of utilizing chlorpyrifos as a sole source of carbon and energy was isolated 21 days after the third chlorpyrifos application, which indicated that the capability of soil microorganism for degrading chlorpyrifos was formed during the experiment. It could be concluded that repeated applications of chlorpyrifos had no lasting impact on soil health.

Characteristics of cadmium uptake and accumulation by two contrasting ecotypes of Sedum alfredii Hance.

The mined ecotype of Sedum alfredii Hance has been identified to be a zinc (Zn) hyperaccumulator native to China. In the present article, the characteristics of cadmium (Cd) uptake and accumulation were compared with hydroponic experiments between the mined and the nonmined ecotypes of Sedum alfredii Hance. The results indicate that the plants of the mined ecotype (ME) have higher tolerance of Cd than the plants of the nonmined ecotypes (NME) in terms of dry matter yield. The thresholds of external Cd levels for the reduction of plant growth were 100 micromolL(-1) for the NME and 400 micromolL(-1) for the ME, respectively. Kinetic study showed that the rates of Cd influx into roots (IR) and transport to shoots (TR) were higher in the ME than in the NME, with 5-fold higher for the maximum IR (Imax) and 13-fold higher for the maximum TR (Tmax) in the NME, respectively. Cadmium concentrations increased with increasing external Cd supply levels. Root Cd concentrations in the NME were higher than that in the ME, with a maximum being 5646 mg kg(-1) for the NME and 2889 mg kg(-1) for the ME at 1000 micromolL(-1) Cd. On the contrary, shoot Cd concentrations of the NME were far lower than that of the ME. Maximum shoot Cd concentrations were 533 mg kg(-1) in leaves and 935 mg kg(-1) in stems at 1000 micromol L(-1) Cd for NME, whereas, 4933 and 3874 mg kg(-1) at 400 micromol L(-1) Cd for the ME, respectively. Meanwhile, Cd concentrations in the shoots of both the NME and ME increased with advancing Cd treatment time. At 100 micromolL(-1) Cd, concentrations of Cd in leaves and stems of the NME sharply increased within initial 8 and 12 days, and those in the ME increased dramatically until D20 and D16, respectively. However, leaf and stem Cd concentrations reached their maximum values on D4 for the NME and D8 for the ME, respectively, when the plants were exposed to 1 micromol L(-1) Cd. Cadmium accumulation by plant shoots was obvious higher in the ME than in the NME at varied Cd supply levels or Cd treatment time. The maximum Cd taken up by the shoots was 1032 microg plant(-1) in concentration-dependent uptake, and 1699 microg plant(-1) in time-course uptake for the ME, with 15-fold and 18-fold higher than those for the NME, respectively. The ratios of shoot/root of Cd ranged from 12 to 39, varying with Cd supply levels, and from 13 to 24 in the varied treatment times for the ME, more than 10 times greater than those for the NME. In addition, Cd distribution in leaves, stems and roots of ME was greatly different from those of NME. The percentage of Cd distribution in shoots was more than 79 at the varied Cd supply levels, or 83 in the varied treatment time for ME, both higher than that for NME. It could be concluded that the mined ecotype of Sedum alfredii Hance has a greater ability to tolerate, transport, and accumulate Cd, as compared with the nonmined ecotype.

Analysis of genetic effects on nutrient quality traits in indica rice.

Nine cytoplasmic male-sterile lines and five restorer lines were used in an incomplete diallel cross to analyze seed effects, cytoplasmic effects, and maternal gene effects on nutrient quality traits of indica rice (Oryza sauva L.). The results indicated that nutrient quality traits were controlled by cytoplasmic and maternal effects as well as by seed direct effects. Maternal effects for lysine content (LC), lysine index (LI), and the ratio of lysine content to protein content (RLP) were more important than seed direct effects, while protein content (PC) and protein index (PI) were mainly affected by seed direct effects. Cytoplasmic effects accounted for 2.41-20.80% of the total genetic variation and were significant for all nutrient quality traits. Additive genetic effects were much more important than dominance effects for all of the traits studied, so that selection could be applied for these traits in early generations.

Accumulation and partitioning of phosphorus and heavy metals in a sandy soil under long-term vegetable crop production.

Increased inputs of phosphorus (P) and heavy metals to agricultural soils have caused considerable concern. Information on accumulation and chemical forms of the elements in soils is needed as a guide for the judicious application of agricultural chemicals and organic manures. The focus of this study was to assess accumulation of P and heavy metals among various fractions of a sandy soil with a 25 year history of vegetable crop production and primarily inorganic fertilization. The results demonstrated that long-term vegetable production practices changed concentrations and partitioning of P and heavy metals in the soil. Phosphorus, Cu, Zn, and Mn were significantly accumulated and moved downward along the soil profile. Most of the total Cr in the vegetable soil accumulated in the upper 0-15 cm. However, there was no significant accumulation and transport of Cd, Co, Mo, Ni, and Pb in the vegetable soil. Major P fractions in the vegetable soil were NaHCO3-P, followed by HCl-P and residual P. Copper, Zn, and Mn accumulated predominantly in the CaCO3 fraction or oxide fraction, whereas Cr accumulated mainly in the organically bound fraction, indicating that P, Cu, Zn, and Mn in the vegetable soil have greater mobility potential. Compared with adjacent forest soil, the vegetable soil had a lower percentage of P, Cu, Zn, and Mn in the residual fractions, and a higher percentage of P, Cu, Zn, and Mn in the CaCO3 fractions or organically bound fraction.

Adsorption-desorption characteristics of lead in variable charge soils.

Adsorption desorption processes of Pb at contaminated levels in two variable charge soils were investigated. The red soil (RAR) developed on the Arenaceous rock (clayey, mixed siliceous thermic typic Dystrochrept) adsorbed more Pb2+ than the red soil (REQ) derived from the Quaternary red earths (clayey, kaolinitic thermic plinthite Aquult). The maximum adsorption values (Xm) that were obtained from the simple Langmuir model were 52.6 mmol Pb2+ kg(-1) soil and 29.9 mmol Pb2+ kg(-1) soil, respectively, for the RAR and REQ. Adsorption of Pb2+ decreased soil pH by 1.10 unit for the RAR soil and 1.21 unit for the REQ soil at the highest loading. The adsorption equilibrium pH of RAR was higher than that of REQ at the same Pb2+ concentration. The distribution coefficient (Kd) of Pb in the soils decreased exponentially with increasing Pb2+ loading. Most of the adsorbed Pb2+ in the soils was not desorbed in the 0.01 mol L(-1) NaNO3 solution. After five successive extractions with NaNO3, only 0-11% of the total adsorbed Pb2+ in the RAR soil was desorbed and the corresponding value of the REQ soil was 0-19%, indicating that the RAR soil had a greater affinity for Pb2+ than the REQ soil at the same Pb2+ loading. Different mechanisms might be involved in Pb2+ adsorption/desorption at different levels of Pb2+ loading and between the two soils.