Tijuana Childhood Lead Risk Assessment Revisited: Validating a GIS Model with Environmental Data

The objective of this research was to determine the spatial distributions of childhood lead poisoning and soil lead contamination in urban Tijuana. The Bocco–Sanchez model of point-source emissions was evaluated in terms of validity and reliability. We compared the model's predicted vulnerable populations with observed cases of childhood lead poisoning in Tijuana, identified fixed point sources in the field, and analyzed 76 soil samples from 14 sites. The soil lead results were compared to the blood lead analyses performed on Tijuana children whose blood lead levels were ≥10 μg/dL, who reported that they did not use lead-glazed ceramics for cooking or storing food (n = 63). Using GIS, predicted vs observed risk areas were assessed by examining spatial patterns, including the distribution of cases per designated risk area. Chi-square analysis of expected vs observed values did not differ significantly at the p = 0.02 level, showing that the model was strikingly accurate in predicting the distribution of subjects with elevated blood lead. Results reveal that while point sources are significant, other sources of lead exposure are also important. The relative public health risk from exposure to lead in an urban setting may be assessed by distinguishing among sources of exposure and associating concentrations to blood lead levels. The results represent an iterative approach in environmental health research by linking environmental and human biomarker lead concentrations and using these results to validate an environmental model of risk to lead exposure.     

Arsenic distribution in Florida urban soils: comparison between Gainesville and Miami

Arsenic contamination is of concern due to its effect as a carcinogen. Understanding the distribution of arsenic in urban soils is important for establishing baseline concentrations from which anthropogenic effects can be measured. The soil cleanup target level (SCTL) for arsenic in Florida (0.8 and 3.7 mg kg(-1) in residential and commercial areas, respectively) is lower than in most states and is near the arsenic background concentrations in Florida soils. The objective of this study was to characterize the distribution of arsenic in the soils of two Florida cities, Gainesville and Miami. More than 200 soil samples were collected from three land-use classes in each city (residential, commercial, and public land), digested with USEPA Method 3051a, and analyzed with graphite furnace atomic absorption spectrophotometry. Arsenic concentrations varied greatly in Gainesville, ranging from 0.21 to approximately 660 mg kg(-1) with a geometric mean (GM) of 0.40 mg kg(-1) (after discarding outliers), which was significantly lower than the GM of 2.81 mg kg(-1) in Miami, although Miami samples ranged only from 0.32 to approximately 110 mg kg(-1). Arsenic concentrations in 29 and 4% of the Gainesville soil samples and 95 and 33% of the Miami samples exceeded the Florida residential and commercial SCTL, respectively. This study is the first to provide information on arsenic distribution in urban soils of Florida, and the data are useful for assessing arsenic contamination and determining the need for remediation.     

ACCUMULATION OF AS,NI, CU,AND PB IN RETENTION AND RECHARGE BASINS SOILS FROM URBAN RUNOFF1

ABSTRACT: The accumulation of arsenic, nickel, copper, and lead in the soil profile was determined beneath five urban storm-water retention/recharge basins used by the Fresno Metropolitan Flood Control District, California. Soils were sampled from the surface to the first zone of saturation and compared with soils from an adjacent un-contaminated control site. These elements were found to be accumulating in the first few centimeters of basin soil and are important to the effectiveness of a specific best management practice, i.e., the retention and recharge of urban storm water. Study basins in use since 1962, 1965, and 1969 had lead contents in the 0–2 cm soil depth interval‘of 570, 670, and 1400 mg Pb/kg soil, respectively. The median indigenous soil lead concentration was 4.6 mg/kg soil. The practice of removing excess flood runoff water from two basins by pumping apparently is a factor in reducing the accumulation rate of these elements in the surface soils of the basins.     

Determination of urinary lead in school children in Manzini, Swaziland, Southern Africa

Two hundred and fifty-seven urine samples collected from school children living in the Manzini region, Swaziland, were analysed for lead (Pb), using a graphite furnace atomic absorption spectrometer. The mean urine lead concentration for the urban schools ranged from 0.038–0.040 gml^–1, while that for the rural schools ranged from 0.017–0.022 gml^–1. The observed range shown by the urban schools was above the normal (for healthy humans) urine lead concentration of 0.035 gml^–1. However, the mean urine lead concentration for the rural schools was found to be lower than this value. The mean urine lead concentration for the urban schools was significantly higher than that of the rural schools. The differences in the mean urine lead concentrations for boys and girls from both urban and rural schools were found not to be significant, despite the higher values shown by the girls. The difference in lead concentrations between urban and rural schools in Manzini was thought to be due to the traffic density within the urban area.     

Evaluation of groundwater contamination beneath an urban environment: the Besòs river basin (Barcelona, Spain)

The urban groundwater of the central Besòs river basin (the La Llagosta aquifer) has become contaminated due to the infiltration of wastewater from septic tanks and sewage networks, and by industrial activities located in urban areas. The groundwater hydrogeochemistry of the La Llagosta aquifer was characterized using isoconcentration maps, hydrogeochemical diagrams (Piper, Schoeller-Berkaloff) and by analyzing hydrogeochemical changes along a flow-path that crosses an urban and peripheral industrial area in the main alluvial aquifer (the La Llagosta unit). The evolution of cations, anions and heavy metals along the flow path and the use of the PHREEQC numerical code indicate a complex set of geochemical processes, which result from the interaction between the sources of pollution, the groundwater flow and the mineral composition of the aquifer materials. The contaminated groundwater below the urban areas shows high contents of NO(3)(-) (90-100 mg/L) and an increase in the concentrations of Ca(2+) and Mg(2+) which coincides with a decrease in pH. The Eh shows greater variation than the pH along the flow line studied, with values ranging between 56 mV in the industrial area and 370 mV in the urban area. The area with the lowest Eh value coincides with the highest concentrations of dissolved Fe (4.7 mg/L) and Mn (0.22 mg/L).     

Analysis of heavy metals and aromatics compounds in soil layers of a sanitary landfill

Solid waste presents the potential for contamination of the soil when it is improperly managed. One of the great challenges of today's society is to promote the proper disposal of municipal solid waste in order to guarantee the safety of public health and to avoid risks to the environment. In this context, the objective of this study is to analyze the concentration profiles of heavy metals and aromatic hydrocarbons of risk that human health in landfill soil. Such works provides an important tool to evaluate the possible presence of contaminants from inappropriate waste disposal, as well as to assist in the management of waste and to prevent environmental contamination. In order to analyze cadmium (Cd), lead (Pb), nickel (Ni), arsenic (As), and mercury (Hg), which are toxic elements, and aromatic hydrocarbons, including benzene, toluene, ethylbenzene, o‐xylene, m‐xylene, and p‐xylene, soil samples were collected at different sites and depths. Neither Cd nor As was detected in any of the samples that were analyzed. Pb levels ranged from 5.34 milligrams per kilograms (mg/kg) to 7.40 mg/kg, Ni levels ranged from 2.17 mg/kg to 3.00 mg/kg, and Hg levels ranged from 75.4 micrograms per kilograms (μg/kg) to 88.3 μg/kg. The aromatic hydrocarbon compounds of benzene, toluene, ethylbenzene, and o‐xylene were below 5.5 μg/kg, and m‐, p‐xylene was below 11 μg/kg. The analysis of heavy metals and aromatic hydrocarbons present in the landfill soil showed concentrations below the soil quality guideline values of the Brazilian National Environment Council (CONAMA) Resolution 420, which has criteria for the presence of chemical substances in soil for Brazil. Therefore, the low levels of chemicals may be related to the operational time of the landfill or to the population profile of the municipality, which is predominantly composed of persons involved in family‐based agriculture.     

Distribution and mobility of mercury in soils of a gold mining region, Cuyuni river basin, Venezuela

An extensive and remote gold mining region located in the East of Venezuela has been studied with the aim of assessing the distribution and mobility of mercury in soil and the level of Hg pollution at artisanal gold mining sites. To do so, soils and pond sediments were sampled at sites not subject to anthropological influence, as well as in areas affected by gold mining activities. Total Hg in regionally distributed soils ranged between 0.02 mg kg(-1) and 0.40 mg kg(-1), with a median value of 0.11 mg kg(-1), which is slightly higher than soil Hg worldwide, possibly indicating long-term atmospheric input or more recent local atmospheric input, in addition to minor lithogenic sources. A reference Hg concentration of 0.33 mg kg(-1) is proposed for the detection of mining affected soils in this region. Critical total Hg concentrations were found in the surrounding soils of pollutant sources, such as milling-amalgamation sites, where soil Hg contents ranged from 0.16 mg kg(-1) to 542 mg kg(-1) with an average of 26.89 mg kg(-1), which also showed high levels of elemental Hg, but quite low soluble+exchangeable Hg fraction (0.02-4.90 mg kg(-1)), suggesting low Hg soil mobility and bioavailability, as confirmed by soil column leaching tests. The vertical distribution of Hg through the soil profiles, as well as variations in soil Hg contents with distance from the pollution source, and Hg in pond mining sediments were also analysed.     

ACCUMULATION OF SELECTED TRACE METALS IN SOILS OF URBAN RUNOFF SWALE DRAINS1

ABSTRACT: Field investigations were conducted at three sites in the Washington, D.C., area to detect the accumulation patterns of the trace metals, cadmium, copper, lead and zinc in the soils of roadside grassed swale drains that had been receiving urban stormwater runoff. Two sites were residential areas and one site was an intensively used highway. The research results seem to indicate that the use of swale drains to control urban stormwater runoff had few harmful effects to fine textured soils with respect to the study metals. With the exception of zinc, typical roadside patterns of decreasing metal concentrations with increasing distance from roads were observed for the upper 5 cm of study soils. Zinc accumulated in residential grassed swales due to leachate from galvanized curverts. Sampling to a depth of 60 cm revealed no evidence of subsurface trace metal enrichment in the study swales. Although the percentage of soil zinc in leachable form was as high as 20 percent of total zinc concentrations, the other study metals had small leachable components. Leachable lead was always less than 1 percent of the total lead.     

ESTIMATING NUTRIENT AND SEDIMENT THRESHOLD CRITERIA FOR BIOLOGICAL IMPAIRMENT IN PENNSYLVANIA WATERSHEDS1

ABSTRACT: This study employs a simple nonlinear statistical approach to establish nitrogen, phosphorus, and sediment concentration and unit area load thresholds to aid in the evaluation of aquatic biological health of watersheds within the state of Pennsylvania. Flow, nitrogen and phosphorus species, sediment, basin area, land cover, and biological assessment data were assembled for 29 Pennsylvania watersheds. For each watershed, rating curves depicting flow versus load relationships were developed using the U.S. Environmental Protection Agency's (USEPA's) storage and retrieval database (STORET) flow and concentration data, then applied to daily flow data obtained from U.S. Geological Survey (USGS) daily flow gauging stations to estimate daily load between 1989 and 1999. The load estimates and concentration data were then sorted into six sets of data: mean annual unit area nitrogen, phosphorus, and sediment loads; and average nitrogen, phosphorus, and sediment concentrations. Results of Mann‐Whitney tests conducted on each of the six datasets indicate that there is a statistically significant difference between the concentrations and unit area loads of nitrogen, phosphorus, and sediment in impaired and unimpaired watersheds. Concentration thresholds, calculated as the midpoint between the impaired and unimpaired watersheds’ 95 percent confidence interval for the median, were estimated to be 2.01 mg/L, 0.07 mg/L, and 197.27 mg/L for nitrogen, phosphorus, and sediment, respectively. Annual unit area load thresholds were estimated to be equal to 8.64 kg/ha, 0.30 kg/ha, and 785.29 kg/ha, respectively, for nitrogen, phosphorus, and sediment species.     

Understanding the impact of waste disposal sites on soil quality for agricultural production: A case study of the Kiteezi landfill,Uganda

Leachate from waste disposal sites (WDS) can significantly affect the soil physical, chemical and biological qualities, reducing soil health and agricultural productivity. However, there is a paucity of data on soil quality for understanding soil health impact due to WDS in Uganda. This study's aim was to understand, using the Kiteezi landfill site, how WDS impact soil properties. Soil samples were collected over 4 months in and around the landfill from three locations, and the soil quality data of the nearby area were used as baseline data for assessing the impact on soil due to WDS in the area. There were significant increases in the concentration of all studied parameters at the landfill except total N. The concentrations of ammonium (14.84 ± 1.76 mg/kg), nitrate (127.96 ± 18.36 mg/kg), and pH (7.8) were above the optimum levels. The levels of available P (181.4 ± 28.9 mg/kg) and exchangeable bases; K (2.23 ± 0.24 mg/kg), Na (1.17 ± 0.14 mg/kg), Mg (3.35 ± 0.3 mg/kg) and Ca (14 ± 1.1 mg/kg) cmol (+)/kg were optimal for plant growth. The calculated CEC of 20.75 cmol (+)/kg) showed that soils have a good potential to supply plant nutrients. Heavy metal levels were still below the permissible limit. Hence, the study shows that although WDS may contribute to the increase of soil fertility, they can potentially reduce the overall productivity of soil by increasing nutrient levels beyond optimum levels.     

Nitrate Concentrations in Springs Flowing into the Lower Flint River Basin,Georgia U.S.A.1

Allums, Stephanie E., Stephen P. Opsahl, Stephen W. Golladay, David W. Hicks, and L. Mike Conner, 2012. Nitrate Concentrations in Springs Flowing Into the Lower Flint River Basin, Georgia U.S.A. Journal of the American Water Resources Association (JAWRA) 48(3): 423-438. DOI: 10.1111/j.1752-1688.2011.00624.x Abstract: Analysis of long-term data from (2001-2009) in four springs that discharge from the Upper Floridan aquifer into the Flint River (southwestern Georgia, United States) indicate aquifer and surface-water susceptibility to nutrient loading. Nitrate-N concentrations ranged from 1.74 to 3.30 mg/l, and exceeded historical levels reported for the Upper Floridan aquifer (0.26-1.52 mg/l). Statistical analyses suggest increasing nitrate-N concentration in groundwater discharging at the springs (n = 146 over eight years) and that nitrate-N concentration is influenced by a dynamic interaction between depth to groundwater (an indicator of regional hydrologic conditions) and land use. A one-time synoptic survey of 10 springs (6 springs in addition to the 4 previously mentioned) using stable isotopes generated δ¹⁵N-NO₃⁻ values (4.8-8.4‰ for rural springs and 7.7-13.4‰ for developed/urban springs) suggesting mixed sources (i.e., fertilizer, animal waste, and soil organic nitrogen) of nitrate-N to rural springs and predominantly animal/human waste to urban springs. These analyses indicate a direct relation between nitrate-N loading since the 1940s and intensification of agricultural and urban land use. This study demonstrates the importance of evaluating long-term impacts of land use on water quality in groundwater springs and in determining how rapidly these changes occur.     

Occurrence of metals in soil and ground water near chromated copper arsenate-treated utility poles

To thoroughly investigate the metal contamination around chromated copper arsenate (CCA)/polyethylene glycol (PEG)-treated utility poles, a total of 189 soil samples obtained from different depths and distances near six treated poles in the Montreal area (Canada) were analyzed for Cu, Cr, and As content. Various soil physicochemical properties were also determined. Ground water samples collected below the poles were analyzed for metals and bioassays with Daphnia magna were conducted. Generally, sandy soils had lower contaminant levels than clayey and organic soils. Copper concentrations in soil were highest followed by As and Cr. The highest Cu (1460 +/- 677 mg kg(-1)), As (410 +/- 150 mg kg(-1)), and Cr (287 +/- 32 mg kg(-1)) concentrations were found at the ground line and immediately adjacent to the pole. Contaminant levels then decreased with distance, approaching background levels within 0.1 m from the pole for Cr and 0.5 m for Cu and As. Chromium and Cu levels generally approached background levels at a depth of 0.5 m. Average As content near the pole on all study sites was three to eight times higher than Quebec's Level C criterion (50 mg kg(-1)), although it dropped to 31 mg kg(-1) at 0.1 m. Results also showed that As persisted up to 1 m in soil depth (17-54 mg kg(-1)). Copper and Cr concentrations in ground water samples were always <1.000 mg L(-1) and <0.05 mg L(-1), respectively and Cr(VI) was <0.02 mg L(-1). One sample contained an As concentration >0.025 mg L(-1) but bioassays showed that, overall, ground water had a low ecotoxic potential.     

Wastewater Effluent,Combined Sewer Overflows,and Other Sources of Organic Compounds to Lake Champlain1

Abstract: Some sources of organic wastewater compounds (OWCs) to streams, lakes, and estuaries, including wastewater‐treatment‐plant effluent, have been well documented, but other sources, particularly wet‐weather discharges from combined‐sewer‐overflow (CSO) and urban runoff, may also be major sources of OWCs. Samples of wastewater‐treatment‐plant (WWTP) effluent, CSO effluent, urban streams, large rivers, a reference (undeveloped) stream, and Lake Champlain were collected from March to August 2006. The highest concentrations of many OWCs associated with wastewater were in WWTP‐effluent samples, but high concentrations of some OWCs in samples of CSO effluent and storm runoff from urban streams subject to leaky sewer pipes or CSOs were also detected. Total concentrations and numbers of compounds detected differed substantially among sampling sites. The highest total OWC concentrations (10‐100 μg/l) were in samples of WWTP and CSO effluent. Total OWC concentrations in samples from urban streams ranged from 0.1 to 10 μg/l, and urban stream‐stormflow samples had higher concentrations than baseflow samples because of contributions of OWCs from CSOs and leaking sewer pipes. The relations between OWC concentrations in WWTP‐effluent and those in CSO effluent and urban streams varied with the degree to which the compound is removed through normal wastewater treatment. Concentrations of compounds that are highly removed during normal wastewater treatment [including caffeine, Tris(2‐butoxyethyl)phosphate, and cholesterol] were generally similar to or higher in CSO effluent than in WWTP effluent (and ranged from around 1 to over 10 μg/l) because CSO effluent is untreated, and were higher in urban‐stream stormflow samples than in baseflow samples as a result of CSO discharge and leakage from near‐surface sources during storms. Concentrations of compounds that are poorly removed during treatment, by contrast, are higher in WWTP effluent than in CSO, due to dilution. Results indicate that CSO effluent and urban stormwaters can be a significant major source of OWCs entering large water bodies such as Burlington Bay.     

大连城市大气中多环芳烃的污染特征和毒性评价

通过对大连市工业区、居民区和城市背景区3种类型区域连续7个月大气样品的采集,分析PAHs在大气中的污染特征,并对其毒性进行评价。结果显示,城市工业区大气中PAHs含量最高,其次是居民区,城市背景区最低。3种类型采样点大气中PAHs的组成相似,菲是含量最多的物质,其次是荧蒽、芴和芘。16种PAHs基于苯并[a]芘的总毒性当量浓度为:工业区5.1 ng/m^3;居民区3.6 ng/m^3;城市背景区4.6 ng/m^3。3种类型功能区大气中PAHs的TEQ值都高于我国的《空气质量标准》(GB 3095-2012)中规定的大气中苯并[a]芘的年平均浓度(1 ng/m^3)或24 h平均浓度(2.5 ng/m^3)。     

Multivariate analysis of trace metal levels in tannery effluents in relation to soil and water: a case study from Peshawar, Pakistan

Tannery effluents and relevant ground water and soil samples collected from various tanning industries of Peshawar were analyzed for Na, Ca, K, Mg, Fe, Mn, Cr, Co, Cd, Ni, Pb and Zn by the AAS method. The metal concentration data for the three media are reported in terms of basic statistical parameters, metal-to-metal correlations and linear regression analyses. Metal distributions in the three media were quite divergent and showed non-normal distributions with high standard deviation and skewness parameters. Sodium exhibited the highest mean levels of 1,277mg/L, 881mg/L and 12,912mg/kg in the effluent, ground water and soil samples, respectively. Among other metals, Cr concentrations were 410mg/L, 0.145mg/L, 100mg/kg and Ca, 278mg/L, 64.8mg/L, and 2,285mg/kg in the effluent, ground water and soil samples, respectively. Some significant correlations were observed between effluent and soils in terms of Na, Cr, Ni, Co and Pb. The ground water-soil interrelationship suggested that Na levels in the soil and ground water were significantly correlated with each other (r=0.486, P<0.01). Similarly, Cr in the soil is strongly correlated with Ca in ground water (r=0.486, P<0.01). These results were duly supported by the linear regression analysis of data. The source identification studies conducted using Principal Component Analysis (PCA) and Cluster Analysis (CA) evidenced that ground water and soil were being contaminated by the toxic metals emanating from the tannery effluents.     

Impacts of urban forests on offsetting carbon emissions from industrial energy use in Hangzhou,China

This study quantified carbon storage and sequestration by urban forests and carbon emissions from energy consumption by several industrial sources in Hangzhou, China. Carbon (C) storage and sequestration were quantified using urban forest inventory data and by applying volume-derived biomass equations and other models relating net primary productivity (NPP) and mean annual biomass increments. Industrial energy use C emissions were estimated by accounting for fossil fuel use and assigning C emission factors. Total C storage by Hangzhou's urban forests was estimated at 11.74 Tg C, and C storage per hectare was 30.25 t C. Carbon sequestration by urban forests was 1,328, 166.55 t C/year, and C sequestration per ha was 1.66 t C/ha/year. Carbon emissions from industrial energy use in Hangzhou were 7 Tg C/year. Urban forests, through sequestration, annually offset 18.57% of the amount of carbon emitted by industrial enterprises, and store an amount of C equivalent to 1.75 times the amount of annual C emitted by industrial energy uses within the city. Management practices for improving Hangzhou's urban forests function of offsetting C emissions from energy consumption are explored. These results can be used to evaluate the urban forests' role in reducing atmospheric carbon dioxide.     

Characterization of pollutants in Florida street sweepings for management and reuse

Disposal and beneficial-use options for street sweeping residuals collected as part of routine roadway maintenance activities in Florida, USA, were assessed by characterizing approximately 200 samples collected from 20 municipalities. Total concentrations (mg/kg or μg/kg) and leachable concentrations (mg/L or μg/L) of 11 metals and a number of organic pollutant groups (volatile organics, semi-volatile organics, pesticides, herbicides, carbamates) in the samples were measured. The synthetic precipitation leaching procedure (SPLP) was performed to evaluate the leachability of the pollutants. From the total metal analysis, several metals (e.g., arsenic, barium, chromium, copper, nickel, lead, and zinc) were commonly found above their detection limits. Zinc was found to have the highest mean concentration of all metals measured (46.7 mg/kg), followed by copper (10.7 mg/kg) and barium (10.5 mg/kg). The metal with the smallest mean concentration was arsenic (0.48 mg/kg). A small fraction of the total arsenic, barium, lead, and zinc leached in some samples using the SPLP; leached concentrations were relatively low. A few organic compounds (e.g., 4,4′-DDT, endrin, and endosulfan II) were detected in a limited number of samples. When the total and leaching results were compared to risk-based Florida soil cleanup target levels and groundwater cleanup target levels, the street sweepings were not found to pose a significant human-health risk via direct exposure or groundwater contamination.     

Polycyclic aromatic hydrocarbon storage in a typical Cerrado of the Brazilian savanna

There may be important biological sources of polycyclic aromatic hydrocarbons (PAHs) to the global environment, particularly of naphthalene, phenanthrene, and perylene, that originate in the tropics. We (i) studied the distribution of PAHs among different compartments of a typical Cerrado to locate their sources and (ii) quantified the PAH storage of this ecosystem. The sum of 20 PAH (sigma20PAHs) concentrations ranged from 25 to 666 microg kg(-1) in plant tissue, 7.4 to 32 microg kg(-1) in litterfall, 206 to 287 microg kg(-1) in organic soil, and 10 to 79 microg kg(-1) in mineral soil. Among the living biomass compartments, the bark had the highest mean PAH concentrations and coarse roots the lowest, indicating that PAHs in the plants originated mainly from aboveground sources. Naphthalene and phenanthrene were the most abundant individual PAHs, together contributing 33 to 96% to the sigma20PAHs concentrations. The total storage of the X20PAHs in Cerrado was 7.5 mg m(-2) to a 0.15-m soil depth and 49 mg m(-2) to a 2-m soil depth. If extrapolated to the entire Brazilian Cerrado region, roughly estimated storages of naphthalene and phenanthrene correspond to 7300 and 400 yr of the published annual emissions in the United Kingdom, respectively. The storage of benzo[a]pyrene, a typical marker for fossil fuel combustion, in the Cerrado only corresponds to 0.19 yr of UK emissions. These results indicate that the Brazilian savanna comprises a huge reservoir of naphthalene and phenanthrene originating most likely from the aboveground parts of the vegetation or associated organisms. Thus, the Cerrado might be a globally important source of these PAHs.     

Nutrients and Heavy Metals in Legacy Sediments: Concentrations,Comparisons with Upland Soils,and Implications for Water Quality

Concentrations of nutrients and heavy metals in streambank legacy sediments are needed to estimate watershed exports and to evaluate against upland inputs. Concentrations of nutrients and heavy metals were determined for legacy sediments in 15 streambanks across northeastern Maryland, southeastern Pennsylvania, and northern Delaware. Samples were collected from multiple bank depths from forested, agricultural, urban, and suburban sites. Analyses were performed for fine (<63 μm) and coarse sediment fractions. Nutrient and heavy metal concentrations were significantly higher in fine than coarse legacy sediments and water extractable nutrient concentrations were significantly greater for fine sediments. Nutrient and heavy metal concentrations were highest in streambank legacy sediments associated with urban land use, but few differences were found with bank depth. Total N (40–3,970 mg/kg) and P (25–1,293 mg/kg) and bioavailable P (0.25–48.8 mg/kg) concentrations for legacy sediments were lower than those for upland soils. This suggests that legacy sediments could serve as sink or source of N and P depending on the redox conditions and stream water nutrient concentrations. However, despite low concentrations, caution should be exercised since streambank erosion and legacy sediment mass loadings could be high, these sediments are in immediate proximity of aquatic ecosystems, and biogeochemical transformations could result in release of the nutrients.     

Heavy metals in an urban watershed in southeastern Michigan

The occurrence of heavy metals in the soil was measured over a period of several years to determine background concentrations in a heavily urbanized watershed in southeastern Michigan. A spatially dispersed sample was collected to capture the inherent variability of the soils and historic land use. The analysis focused on 14 metals (antimony, arsenic, barium, beryllium, cadmium, chromium, copper, lead, mercury, nickel, selenium, silver, thallium, and zinc) that are part of the USEPA's list of the 129 most common pollutants. Metal concentrations were measured at three depths: near-surface (<0.5 m), shallow subsurface (0.5-10 m), and depths greater than 10 m across six soil units in glacial terrain. Additional analyses assessed the metal concentrations in each depth profile across three general land use categories: residential, commercial, and industrial. Metal concentrations were the highest in the near-surface with Pb present at concentrations averaging 15.5 times that of background in industrial areas and approximately 16 times background in residential areas. Cadmium, Hg, and Zn were also present in surface soils at levels of several times that of background. The highest concentrations of each of these metals were present in the clay-rich soils located in the eastern, more urbanized and industrialized part of the watershed. Metals detected at elevated concentrations decreased in concentration with increasing depth and distance from the urbanized and industrialized center of the watershed. Statistically significant differences in the concentrations of heavy metals were also noted between the land use categories, with Cd, Cr, Cu, Pb, Ni, and Zn observed within industrial areas at mean concentrations several times greater than background levels.