Sulfur and heavy metals Total and available soil elements Urban–rural gradient South China

Environ Monit Assess(2009)154:263–274DOI10.1007/s10661-008-0394-3Concentrations of sulphur and heavy metals in needles and rooting soils of Masson pine(Pinus massoniana L.) trees growing along an urban–rural gradientin Guangzhou,ChinaFang Fang Sun·Da Zhi Wen·Yuan Wen Kuang·Jiong Li·Ji Guang ZhangReceived:30January2008/Accepted:05May2008/Published online:21June2008©Springer Science+Business Media B.V.2008Abstract Current(C)and previous year(C+1) needles and soils(organic horizon,0–10cm and 10–20cm mineral depth)of Masson pine(Pinus massoniana L.)trees were sampled at four forested sites(Huang Pu industrial district,HP; South China Botanical Garden,BG;Mao Feng Mt.,MF;and Nan Kun Mt.,NK)in Guangzhou along a urban-rural gradient and analyzed for sul-fur(S)and heavy metals(Cu,Zn,Ni,Cd,Cr and Pb)concentrations.Needle concentrations of all the elements were significantly higher at industrial HP than at other three sites,except for Cu and Pb which were highest at the traffic site(BG).The C+1needles generally had higher Cu,Cd,Pb, Zn,Cr than the C needles while the opposite was for Ni and S.Total and available Cd,Pb,Zn in soils peaked at the urban sites(HP and BG)and decreased at suburban MF and rural NK.Heavy metals were generally higher in the organic soils than in the mineral soils at all sites.Zinc and F.F.Sun·D.Z.Wen(B)·Y.W.Kuang·J.Li·J.G.ZhangInstitute of Ecology,South China Botanical Garden,The Chinese Academy of Sciences,Xingke Rd.723,Tianhe District,Guangzhou510650,Chinae-mail:dzwen@F.F.Sun·J.G.ZhangGraduate University of the ChineseAcademy of Sciences,Beijing100049,China Pb at all sites,and Cd,S and Cu at the urban sites(HP and BG)in soils or pine needles were above or near their respective natural background levels,implying that threats resulted from these toxic elements occurred on local particularly ur-ban forests,but did not for Cr and Ni due to their presence below their background values.Our re-sults demonstrated that elements concentrations in needles and soils had reflected the variability of pollutants and the environmental quality change along the urban–rural transect,and were efficient as biomonitors to assess the influence of anthro-pogenic activities along the urbanization course on forest health.Keywords Sulfur and heavy metals·Total and available soil elements·Pinus massoniana·Bio-monitoring·Urban–rural gradient·South China IntroductionIncreasing urbanization and industrialization cou-pled with other anthropogenic activities have imposed unprecedented disturbance and suppres-sion on urban forest ecosystems and their sur-roundings of the Pearl River Delta of China(Hu and Su1999;Luo and Xu2001;Wong et al.2002; Yuan2002).Emissions of various harmful sub-stances including acid precursors and heavy met-als into the environments and their subsequent impacts on ecosystems have become increasingly serious problems in this region(Florig1997;Yuan 2002;Zhou et al.2004).Sulphur and heavy metals deposition not only affected the nutrient status of conifer needles and in extreme cases led to death of plants,but also created a threat to animals and humans(Yilmaz and Zengin2004).Growing con-cern over the potential ecotoxicological hazards has prompted reliable,low cost methods for as-sessing the extent of contamination on local envi-ronment and the exposure risk to both plants and human beings.One of the most frequently and widely used methods to monitor air pollution was determination of trace elements in plants.Conifer species including Scots pine(Pinus sylvestris L.; Wentzel1982;Giertych et al.1997;Yilmaz and Zengin2004),Norway spruce(Picea abies(L.) Karst.;Fober1976;Ceburnis and Steinnes2000), Canary Island pine(Pinus canariensis C.Sm.; Tausz et al.2005)and Austrian pine(Pinus nigra Arn.;Coskun2006)have been widely accepted for monitoring airborne pollutants as the waxy surfaces of needles can accumulate gaseous pol-lutants and polluting particulates(Al-Alawi and Mandiwana2007).Although a number of studies demonstrated that concentrations of elements in pine needles and urban soils were successfully used to indicate the pollution status(Gratton et al. 2000;Tausz et al.2005;Mingorance et al.2007), most of them focused mainly on needles or total amount of heavy metals in the soil.In fact,the severity of pollution depends not only on total heavy metals in the soil,but also on their mobile and bio-available proportions,which are generally controlled by the texture and other physicochem-ical properties of the soils(Ma and Rao1997).Being one of the fast growing regions where China open-door policy and economic reforms with special regulations and taxation to attract foreign investments were implemented since late 1970s,Guangzhou has undergone a rapid transi-tion from a traditional agriculture-based economy to an increasingly industry-and technology-based economy.Thereafter,expansion of industries and urbanization coupled with high acid rain fre-quency,rapid soil acidification,heavy metal soil contamination,water pollution and vegetation damages in this region were emerged(Zhang 1999;Wong et al.2002;Cheung et al.2003;Wen et al.2006).It was estimated that forests with a total area of254,943ha were affected by acid rain and volume losses of conifer forests was98,740m3 per year in Guangzhou(Hu and Su1999).Recent data showed that the mean annual SO2concen-tration was0.057mg m−3during the1998–2006 (Guangzhou Environmental Protection Bureau 1999–2007)and about71.8%of the rainfalls were acid rain and the mean pH value of precipita-tion was4.53during the1996–2005(Wu2006). Guan and Peart(2006)confirmed the usefulness of leaves to monitoring the traffic pollution by an-alyzing plant leaves and soils collected from road-side,urban garden and a university in Guangzhou. However,the study neglected the possible effects of industrial emissions and the relative role of the available portions of soil metals for plants uptake.This study was carried out as part of the Urban–Rural Environmental Change Project,with the aims of investigating the variability of pollutants and environmental quality change,and character-izing the magnitude of sulphur and heavy metals contamination by sampling and analyzing needles and soils of Masson pine trees along the urban-rural gradient.Concentrations of sulphur(S)and heavy metals(Cu,Cd,Pb,Zn,Cr and Ni)in pine needles were determined.Total amount and avail-able fractions of these elements in soils beneath the pine trees were also analyzed.Materials and methodsDescription of sampling sitesGuangzhou,located in112˚57 –114˚3 E and 22˚26 –23˚56 N,is the capital and the political and economical center of Guangdong province.It has a total area of3,500km2with a population of7.38million in2004.The area is characterized by subtropical monsoon climate with southwest prevailing wind in summer and north wind in win-ter.The mean annual temperature is about21.5˚C. The annual precipitation ranged from1,689.3–1,876.5mm,with a distinct pattern of wet(April through September)and dry(October through March)seasons(Yu and Ng2007).Four forested sites located in Huang Pu indus-trial district(HP),South China Botanical Garden (BG),Mao Feng Mountain(MF)and Nan Kun Mountain(NK)were selected along the north-east direction across Guangzhou for sampling.HP represents the industrial center and the most pol-luted site where the electroplating,aluminum and copper refining factories,and the largest petro-chemical manufacturing plant were situated.BG is situated on the outskirts of Guangzhou,near a traffic road,with traffic loadings of22,300vehi-cles per day in2006(see http://www.gzitransport. com.hk/chi/finan/annual.htm for more informa-tion).MF is a suburban zone,receiving no direct pollution resources.NK is a natural reserve,90km away from the center of Guangzhou,and con-sidered as the remote rural area.The soil type at all sample sites is lateritic red soil that is devel-oped from granite and sand shales(Guangdong Soil Survey Office1993).Sampling and preparationThe needles and rooting soils of Masson pines were collected at the four forested sites along the urban–rural transect in late August and early September2006.Five mature trees of similar size and about40years old without apparent injury and at least100m away from each other were selected for sampling at each site.Current(C, 2006)and previous year needles(C+1,2005) were collected from outer branches of the middle canopy at south,west,east,and north directions, and pooled by needle age for each tree.Soils were collected from the rooting zone at the same four directions with a distance of80cm away from the sample tree,and pooled into organic layer and mineral layers(0–10cm and10–20cm).In laboratory,the sampled needles were gently washed with tap water and rinsed with deionized water to remove the fraction deposited on needle surfaces(Raitio1995;Kos et al.1996),since we focused on the physiologically active fraction of the elements absorbed in the needles rather than the fraction just on the needle surfaces.Addi-tionally,the reference background and threshold values of the elements in the following discussion were the proportions absorbed by pine needles. Then the samples were dried at65˚C to constant weight,ground intofine powder and stored in plastic vials for chemical analyses.Soil samples were air-dried,ground and sieved through2mm and100mesh for available and exchangeable el-ement analyses and total concentration analyses, respectively(Liu1996).Chemical analysesConcentrations of needle heavy metals(Cu,Cd, Pb,Zn,Cr and Ni)were determined by induc-tively coupled plasma atomic emission spectrom-etry(ICP/AES,Optimal2000,USA)after the samples were wet digested with concentrated ni-tric and perchloric acid(8:1,v/v).Total needle sulphur analyses were carried out by a sulphur analyzer(LTDL-9,China).Soil samples were wet digested with concen-trated HF+HNO3+HClO4(4:7:1,v/v),and then determined for total Cu,Pb,Zn,Cr,Ni by ICP/AES(Optimal2000,USA),and for total Cd by graphite furnace atomic absorption spectrome-try(GF-AAS,Zeenit60,German).Total sulphur in the soils was measured by the sulphur analyzer (LTDL-9,China).Available Cu,Cd,Pb,Zn,Cr, Ni in the soils were extracted with0.1M HCl(10g soil sample/50ml HCl extractant),shaked for 1.5h(Scientific Research Cooperation Group of Environmental Pollution Analysis Method1987) and then determined by ICP/AES(Optimal2000, USA).Available S in the soils was determined by barium sulphate nephelometry.The concentra-tions of all the measured elements were expressed as parts per million(ppm=mg kg−1)in dry mass.Data quality was controlled by the national standard reference material(GSV-3for vegeta-tion and ESS-3for soil)supplied by China Nation-al Environmental Monitoring Center.Calibration graphs were obtained by a linear calibration model using eight working elemental standard solutions(WAKO Pure Chemical Industries Ltd., Japan).The obtained calibration graphs were ex-cellent with the correlation coefficient r2>0.999.Statistical analysisSPSS15.0for Windows was used for the data analysis.The standard deviations of the meanswere calculated to compare significant differences between sites.The differences of element concen-trations between the two needle age classes were evaluated by Student’s t test.The mean element concentrations in the needles and soils at each site were calculated,then were used to assess the correlations of concentrations in the needles and soils by Spearman tests(n=4).To further deter-mine the statistical difference between different sites,F test(ANOVA)has been performed at the confidence level of P<0.05.ResultsConcentrations of elements in needlesAs shown in Table1,the mean concentrations of the selected elements in the pine needles were generally followed the order of S>Zn>Pb,Cu, Ni>Cr>Cd.Chromium concentrations were five times as that of Cd.All the elements followed a similar pattern in both needle types that highest concentrations were recorded in the urban sites, and then decreased along the suburban to rural sites(Fig.1).Sulphur concentrations in the C and C+1 needles at the four forested sites along the urban–rural transect ranged from1,740to3,080and from1,580to2,475mg kg−1,respectively,and the highest concentrations in both needle types were recorded in the most polluted site(HP),and lowest in the remote rural area(NK).Cadmium, Pb,Zn and Cr in the C+1needles,and Cd in C needles were significantly higher at the industrial site HP than at the remote site NK,though the highest Pb and Cu in C and C+1needles and highest Ni in the C needles occurred at the BG. Generally,the C+1needles had higher concen-trations of Cu,Cd,Pb,Zn,Cr than the C needles, especially significant for Pb and Zn(P<0.01; Table1).By contrast,Ni and S concentrations were higher in the C needles than in the C+1 needles,particularly significant for Ni(P<0.001; Table1).Concentrations of elements in soilsAs shown in Figs.2and3,elements in soils at the four sites along the gradient followed similar patterns as those in the needles.All the deter-mined elements showed higher concentrations in the urban soils than in the suburban and rural soils except that Cr and Ni concentrations in the suburban soils were higher.Both Zn and Cd in total and available concentrations,were highest in the soils at the industrial site HP,while highest Pb in the soils at the heavy traffic site BG.Total concentrations of Cu,Pb,Zn,Ni and S in the organic layer were significantly higher than those in the mineral layers.However,no signifi-cant difference of total concentrations of elements was observed between upper(0–10cm)and lower (10–20cm)mineral soils.Table1Ranges and mean values of Cu,Cd,Pb,Zn,Cr,Ni and S(mg kg−1)of C(current year)and C+1(previous year) needles(n=20)C needles C+1needles t P valueRange(min–max)Mean Range(min–max)MeanCu 3.37–5.85 4.58 3.42–10.11 5.38−1.93NSCd0–0.500.180–0.370.18−0.04NSPb0.41–10.47 3.48 1.52–12.61 6.56−2.95<0.01 Zn16.52–76.4640.6718.40–81.0954.46−3.15<0.01 Cr0.68–1.98 1.370.18–2.50 1.54−0.90NSNi 1.49–9.25 4.60 1.24–5.51 2.85 3.92<0.001 S1,740–3,0802,1751,580–2,4751,879 2.01NST and P values indicate the significance of differences between the element concentrations in the two needled age classes NS statistically not significantof heavy metals(a,Cu; b,Cd;c,Pb;d,Zn;e,Cr; f,Ni)and sulphur(g)in needles of the current (C)and the previous(C+1)year(means and SD;n=5).Different letters indicate significant differences(P<0.05)in needles at the same age among different sites.HP, BG,MF,and NK stand for Huang Pu industrial site,urban roadside site—South China Botanical Garden, suburban Mao Feng Mountain,and ruralNan Kun Mountain, respectivelyCu(mgkg-1)Cd(mgkg-1)Pb(mgkg-1)Zn(mgkg-1)Cr(mgkg-1)S(mgkg-1)Ni(mgkg-1)Sites SitesHP BG MF NKSitesHP BG MF NKSitesHP BG MF NKSitesHP BG MF NKSitesHP BG MF NKSitesSimilarly,the available fractions of all the heavy metal elements except Cr in organic soils were also significantly higher than those in the mineral soils.Furthermore,available Cu,Cd and Ni in the upper mineral soils were significantly higher than in the lower mineral soils(P<0.05).The percentages of available Cr and Zn among their respective total concentrations were very low,with the range of0.06–0.30%and0.30–1.34%,respectively(Table2).However,the available Cd was extremely high and reached maximum value of81%of the total at some site.Plant–soil relationshipsNeedle Zn concentration was significantly cor-related with soil total Zn while needle Cd with soil available Cd in the0–10cm soils.Needle Pb concentration was correlated with both available concentration in the organic layer and total con-centration in the10–20cm layer(Fig.4).The ratios between needle and available soil concentrations among the four sampling sites were in the order of Pb<Cu<Cd<Ni<S,Cr, Zn.The lowest ratio values were0.59–4.00for Pb,heavy metals(a,Cu;b, Cd;c,Pb;d,Zn;e,Cr;f, Ni)and sulphur(g)in organic(O)and mineral (0–10cm and10–20cm) (means and SD;n=5). Different letters indicate significant differences (P<0.05)between the sites within the same soil layer.Horizontal dotted lines indicate natural background values in soils of elements according to China National EnvironmentalMonitoring Center(1990) and Guangdong Soil Survey Office(1993)Pb(mgkg-1)Zn(mgkg-1)Cd(mgkg-1)Cu(mgkg-1)S(mgkg-1)Cr(mgkg-1)Soil layer Soil layerSoil layerSoil layerSoil layerwhereas the ratios for Zn in the0–10cm and10–20cm layers exceeded100(Table3).The ratios of needle Cu,Cd,Ni and S to their available soil concentrations in the mineral soils and Cr to the available soil concentration in all soil layers at the industrial site HP were higher than those at other sites,while the ratio for Zn was higher at the heavy traffic site BG,particularly in the mineral soils.DiscussionElement concentrations in needlesOur results showed that the C+1needles had significantly higher Pb and Zn concentrations than the C needles did,suggesting that the accumu-lation of these heavy metals in the needles in-creased with the increase of the needle longevityFig.3Availableconcentrations of heavy metals (a,Cu;b,Cd;c,Pb;d,Zn;e,Cr;f,Ni)and sulphur (g)in the organic (O)and mineral (0–10cm and 10–20cm)soils (mean and SD;n =5).n .d .not determined;different letters indicate significant differences at the confidence level of P <0.05among the sitesSoil layer Soil layerSoil layerSoil layerSoil layerO0-10 cm10-20 cmSoil layerO0-10 cm10-20 cmSoil layerZ n (m g k g -1)C d (m g k g -1)P b (m g k g -1)C u (m g k g -1)C r (m g k g -1)N i (m g k g -1)S (m g k g -1)and the exposure time,which were consistent with previous studies that some toxic elements could be accumulated with needles age (Blanuša et al.1999).However,Ni concentration decreased from the C needle to the C +1needle,which was assumedly attributed to its being phloem-mobile element and resorption from older to younger needles as the needles aged (Rautio and Huttunen 2003),or due to the slowing-down accumulation as the foliar nutrient uptake capacity decreased with age (Marschner 1995).This result further confirmed that the old needles were more efficient for monitoring heavy metals than the younger ones (Kuang et al.2007).Masson pines growing at the industrial site HP had the highest concentrations of most elementsTable2Available element concentrations as percentage of the total along the urban–rural gradienta HP,BG,MF,and NK stand for Huang Pu industrial site,urban roadside site—South China Botanical Garden, suburban Mao Feng Mountain,and rural Nan Kun Mountain, respectivelySite a Available fraction percent of totalCu Cd Pb Zn Cr Ni S Organic layer HP20.9521.8016.07 1.340.0910.94–BG16.4430.6219.84 1.240.1614.46 3.94MF 6.7512.9017.860.920.137.15 5.88NK20.7064.8012.86 1.090.1949.73 4.19 0–10cm HP12.2127.829.440.480.08 6.67 4.20 BG20.7663.8116.200.360.20 5.6519.12MF12.3427.2416.270.440.13 3.1013.55NK25.1324.10 4.090.390.2511.3919.05 10–20cm HP7.4527.917.500.330.06 2.578.91 BG24.7480.8610.010.320.20 3.3437.23MF12.5620.6516.480.460.14 2.2840.13NK23.3728.96 2.980.300.3025.7647.53in the needles,followed by those at the subur-ban and rural sites,indicating that urban area received larger amounts of atmospheric pollutants inputs than the remote rural area,and the needle chemical concentrations had reflected the anthro-pogenic emission gradient.The high Pb and Cu concentrations in the pine needles at BG could be related to the heavy traffic loading,since ve-hicular emissions could significantly result in high levels of heavy metals in the needles(Celika et al. 2005;Al-Alawi and Mandiwana2007)or due to the atmospheric transportation and deposition of pollutants from the industrial sites into BG by the prevailing southwest wind during the summer and early autumn seasons.The results also demon-strated that Masson pines growing along the urban-rural gradient provided a natural labora-tory for environmental quality study and reflected the ecological footprints of the anthropogenic ac-tivities along the urbanization course.At all sites,needle Zn exceeded its background reference value(40.0mg kg−1)in Pinus Massoni-ana in Guangzhou(Li and Zheng1989).Needle Pb was close to or higher(particularly at BG) than its normal range(less than10mg kg−1) in plants(Kabata-Pendias and Piotrowska1984). According to the normal concentration(0.01 to0.3mg kg−1)in unpolluted natural stands reported by Allen et al.(1974),needle Cd was within its normal range at all other sites but ap-proached at risky level at industrial site HP with 0.336mg kg−1for C needles and0.298mg kg−1 for C+1needles.These results suggested that Zn contamination and its subsequent phytotoxicity occurred along this gradient,particularly near the urban industrial center,while Pb and Cd pollution were most likely be extended from urban to its larger surrounding areas.Concentrations of Cr and Ni in pine needles were far below the critical values of plants(5–10mg kg−1for Cr,25–40mg kg−1for Ni;Cicek and Koparal2004)and needle Cu was also lower than the background value of11.0mg kg−1(Li and Zheng1989),indicating that Cr,Ni and Cu at their current levels had not posed threat to the health of Masson pines in this region.Sulphur as an important nutrient is taken up as sulphate from the soil,but this uptake is well regulated and will not lead to high foliar S con-centrations(Tausz et al.2005)and the S normal level ranged from10to150mg kg−1for plants (Kacar1970).In the present study,sulfur con-centrations in pine needles at the four sites were surprisingly high,suggesting that large amount of SO2from industrial sources were involved.Earlier work showed that sulphur concentrations of more than1,200mg kg−1dry weight in the C needles and over1,500mg kg−1in the C+1needles were indicative offield plots impacted by sulphur air pollution(Austrian Federal Law1984).Recently, sulphur contents in soil and leaves had been suc-cessfully used to develop correlations between sulphur deposition and needle sulphur concen-trations in European ICP forest monitoring pro-gramme(De Vries et al.2000)and monitor SO2 deposition near a thermal power plant(Cicek andFig.4Relations between needle Cd,Pb and Zn concentrations and soil concentrations(n=4). (a)Needle Cd concentrations vs available Cd concentrations at the0-10cm soils(S avail−sur);(b)Needle Pb concentrations vs available Pb concentrations at the organic soils(S avail−O); (c)Needle Znconcentrations vs total Zn concentrations at the0-10cm soils(S total−sur);(d)Needle Pb concentrations vs total Pb concentrations at the10-20cm soils(S total−deep)Cd avail-sur (mg kg-1).007.008.009.010.011.012.013Cdneedles(mgkg-1)Pb avail-O (mg kg-1)2468101214Pbneedles(mgkg-1)Pb total-deep (mg kg-1)152025303540455055Pbneedles(mgkg-1)Zn total-sur (mg kg-1)889092949698100102104Znneedles(mgkg-1)Koparal2004).Our results showed that S contents in pine needles were highest at urban industrial site,decreased along the gradient,reflecting the variation of sulphur deposition along this gradient affected by the urbanization and industrialization course,which imposed a threat to vegetation and local environment in this region.Soil element concentrationsCompared with the background value of each element in surface soils in Guangdong province (China National Environmental Monitoring Cen-ter1990;Guangdong Soil Survey Office1993),Zn increased in all soil layers at all sites,Cd,Pb and S were also at high levels in the organic soil at all sites except for the rural site NK.The results were consistent with those in the needles,further confirmed the potential threat of Pb,Zn,Cd and S in this region.Element concentrations in the surface soil hori-zon could be used to reflect the different sources of elements(Alloway1990).The higher concen-trations of total and available elements in the soils of urban sites than those in remote area in the present study confirmed that the samples obtained from the urban industrial site and the urban roadside had the highest accumulation of most heavy metals(Celika et al.2005),suggesting that anthropogenic emission was the main inputs of heavy metals in the urban soils.Moreover,significant decrease of both avail-able and total element concentrations from the organic layer to the mineral layers(Figs.2and 3)indicated the higher capacity to retain the at-mospheric deposition by the organic matter and relatively high acidity,which were proved by Lindroos et al.(2007).In mineral layers,the en-richment of available Cu,Cd and Ni in upper layer(0–10cm)might directly result from anthro-pogenic pollutants.However,the total elementTable3Ratios between the needle(N)and available element concentrations(S avail)along the urban–rural gradientSite a Cu Cd Pb Zn Cr Ni SN/S avail(O)HP 3.48 5.620.9344.51148.847.66–BG 6.35 5.620.7745.7725.53 6.7452.82MF 6.137.400.9359.8081.169.0652.18NK 6.09 2.130.5939.1539.219.20145.02 N/S avail(0–10cm)HP12.4824.89 2.34133.25215.0339.29266.81 BG11.5920.15 1.04163.3723.7335.5547.62MF9.3217.96 1.05125.9078.4723.3749.22NK8.789.86 3.04120.2928.5229.9574.13 N/S avail(10–20cm)HP23.2759.71 2.90178.51275.0299.10205.25 BG15.6432.46 1.97186.5825.7257.9818.51MF11.0327.94 1.11117.8477.2334.9321.03NK9.6513.37 4.00150.5825.4341.3332.59 a HP,BG,MF,and NK stand for Huang Pu industrial site,urban roadside site-South China Botanical Garden,suburban Mao Feng Mountain,and rural Nan Kun Mountain,respectivelyconcentrations were not significantly higher in0–10cm layer than those in the10–20cm layer, which was in contrast to a number of studies that revealed the decline in heavy metal concentra-tions with soil depth(Imperato et al.2003)but consistent with Guan and Peart(2006).This could be attributed to high background element concen-trations in the soil,which might mask the small variations of external inputs between different layers.Plant–soil relationshipsThe ratio between the needle and the available soil concentrations is an index of element soil–plant transfer(Baker1983).The low ratio val-ues for Pb,Cd and Cu,accompanied with their high availabilities in soils indicated low Pb,Cd and Cu translocation from soils to needles.De Nicola et al.(2003)ascribed the limited Cd and Pb mobility to the elements being blocked im-mediately after absorption.On the other hand, the high ratio between needle Zn and available soil Zn concentrations,together with its low soil availability suggested that high Zn translocation occurred from soils to needles.The ratio of needle element concentration to its available soil concentration means the capacity of absorbing and accumulating this element.The generally higher ratio values for S and heavy metal in the urban sites suggested that the Masson pines grown in the urban sites could absorb and accu-mulate more heavy metals and S given the same level of soil available element.We assumed that the excess might result from direct uptake from the air.The limited Pb translocation together with the statistically significant correlation between needle and total soil Pb amounts suggested that both canopies and soils were affected by Pb airborne deposition.ConclusionsThe present study attempted to investigate the variability of pollutants and environmental quality change and characterize the magnitude of sul-phur and heavy metals contaminations along the urban-rural gradient in Guangzhou by analyzing needles and soils of Masson pine trees.Interpre-tations from the results indicated that the samples collected from urban sites had higher potentials of sulphur and heavy metals accumulations and anthropogenic emission was the main source of heavy metals into the environments.Levels of the selected elements in needles and soils of Masson pine trees were indicative of the variability of pollutants and environmental quality changes and were efficient for tracing the ecological footprints。