Typical Background Levels Research Articles

Human health risk assessment of heavy metals in residential soil-Houston, Texas.

Human health risk assessment increasingly recognizes the need to integrate participatory-based research, geospatial analysis, and environmental epidemiology, particularly to address contamination concerns in underserved and disadvantaged communities. Here, we demonstrate the combined application of such methods within the Greater Fifth Ward neighborhood in Northeast Houston. In particular, in tandem with community members, we collected soil samples from 193 residential sites using a complete canvassing method from July to November 2021 to characterize contaminant concentrations, focusing on heavy metals and metalloids As, Ba, Cd, Cr, Pb, Se, Ag, and Hg measured using Inductively Coupled Plasma-Mass Spectrometry. Individual heavy metals as well as cumulative cancer and non-cancer risks were calculated for children and adults using the USEPA Regional Soil Screening Levels and benchmarks for specific land uses, such as crop growing. Soils from most sites had low or typical background levels expected in urban areas, but samples from several locations had significantly elevated lead levels (>1200 mg/kg) that warrant additional examination. Geospatial analysis suggested clustering of heavy metal contaminants within one geographic area of the neighborhood. This study highlights how participatory research in underserved environmental justice communities can help characterize current conditions as well as establish priorities for future investigation.

Exploratory measurements of ambient air quality in a residential area applying a diffusion charge based UFP monitor/Orientierende Messungen der Luftqualität in einem Wohngebiet mit einem auf Diffusionsaufladung basierten UFP-Monitor

In the context of the revision of the EU Ambient Air Qualitiy Directive (2008/50/EC), measurement of ultrafine particles (UFP) in ambient air is proposed and discussed. To investigate the local ambient UFP concentration (immis- sion), exploratory measurements of air pollution with UFPs were performed over several months in a residential area. The measurement device is based on charge detection of the measurement aerosol (AQ Guard Smart 2000 of the manufacturer Palas®). The background particle concentrations are within the typical background level for rural residential areas (3,000 to 5,000 cm-3). Increased UFP concentration levels were predominantly measured during the evening and the night. On 53 days of the total measurement duration of 101 days increased par- ticle concentrations above the background level (at least 6,000 cm-3) regarding the 15-minute average values were measured for at least one hour during the evening and night (16:00 to 0:00). The main source of the increased particle concentra- tion is the operation of woodstoves in the neighbourhood of the measuring location. This air pollution in the evening hours is not reflected in the context of daily or monthly averages. Other pollution sources (barbecue, new-years fireworks, traffic – different measurement location) were also identified and differences of the mean particle diameter of the ambient aerosol with regards to the background level (80 nm) could be determined. The device is suitable for UFP measurements and offers a lower detectable size-range compared to conventional scattered-light based optical particle counters.

Ecological Assessment, Spatial Analysis, and Potential Sources of Heavy Metals (HMs) in Soils with High Background Values in the Lead-Zinc Mine, Hezhang County, Southwestern China

The heavy metals (HMs) usually have high natural background levels in lead-zinc mines. Strengthening the ecological risk assessment and accurate identification sources of HMs is an important component of land resource utilization and food security. A total of 795 soil samples (with a depth of 0~20 cm) were collected in Hezhang County, an area of typical high background levels of HMs with more than 18 large lead-zinc deposits. In this study, inductively coupled plasma emission spectrometry (ICP-OES), inductively coupled plasma mass spectrometry (ICP-MS), atomic fluorescence spectrometry (AFS), and the potentiometric method (POT) were used to test the total concentration of HMs and pH values. The geographic information system was used to model the concentration distribution of HMs, and the ecological risk was assessed according to the source analysis results. The results suggest that: (1) the mean concentration of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were 24.55, 2.25, 176.4, 89.6, 0.19, 64.2, 102, and 257 mg·kg−1, respectively, which exceeded the average background value of soils in Guizhou Province by 1.23, 3.41, 1.84, 2.80, 1.73, 1.64, 2.90, and 2.58 times, respectively, and the average concentrations of Cd, Cr, Cu, Ni, Pb and Zn exceed the screening values specified in soil contamination risk in agricultural land; (2) the results of enrichment factor (EF) showed that 29.73% of Cd are moderately polluted, and other HMs were slightly polluted in a small area or near the baseline value (EF ≈ 1); and (3) PMF analysis showed that there are five main sources, pyrite, lead-zinc ore, basalt, carbonate rock, and agricultural production, with the risk contribution ratios of 5.25%, 27.37%, 28.94%, 17.91%, and 20.53%, respectively.

Evaluation of Radiofrequency and Extremely Low-Frequency Field Levels at Children's Playground Sites in Greece From 2013 to 2018.

From 2013 to 2018, in-situ measurements of radiofrequency (RF) electromagnetic fields (EMF) and extremely low-frequency (ELF) electric and magnetic fields in 317 existing and under-construction children's playground facilities, in 16 municipalities all over Greece, were carried out by the Greek Atomic Energy Commission (EEAE). These measurements were conducted following legislative framework established in 2009, which requires that compliance with the established exposure limits for EMFs should be verified in playground areas. The results are presented by the value of the electric field (E) and exposure ratio (Λ) for the RF EMF, as well as the value of the electric field (E) and magnetic flux density (B) for the ELF electric and magnetic fields. Statistical analysis tools were applied on measurement data and conclusions have been made, taking into consideration: (i) environment type (urban/suburban), and (ii) vicinity to any transmitting installations. Measurement results correspond to the typical EMF background levels for each environment type. Concerning the environment type, RF EMF, and ELF electric/magnetic field measurements reveal no differentiation between urban and suburban environments. Bioelectromagnetics. 2019;40:602-605. © 2019 Bioelectromagnetics Society.

Morpho-Physiological and Metal Accumulation Responses of Hemp Plants (Cannabis Sativa L.) Grown on Soil from an Agro-Industrial Contaminated Area

Hemp is a promising plant for phytomanagement. The possibility to couple soil restoration to industrial crop cultivation makes this plant attractive for the management of contaminated sites. In this trial, Cannabis sativa L. plants were grown in a greenhouse on soils from two sites of “Valle del Sacco” (Lazio Region, Italy), a wide area contaminated by agro-industrial activities. One site was representative of moderate and diffuse metal(loid) multi-contamination, above the Italian concentration limit for agriculture (MC—moderately contaminated). The second site showed a metal(loid) content below the aforementioned limit, as a typical background level of the district (C—control). After 90 days, biometric and physiological parameters revealed satisfactory growth in both soil types. MC-grown plants showed a slight, but significant reduction in leaf area, root, and leaf biomass compared with C-grown plants. Chlorophyll content and chlorophyll fluorescence parameters, namely the quantum yield of primary photochemistry (Fv/Fm) and the Performance Index (PIABS), confirmed the good physiological status of plants in both soils. Metal(loid) analyses revealed that As, V, and Pb accumulated only in the roots with significant differences in MC- and C-grown plants, while Zn was found in all organs. Overall, preliminary results showed a satisfactorily growth coupled with the restriction of toxic metal translocation in MC-grown hemp plants, opening perspectives for the phytomanagement of moderately contaminated areas.

Iron oxides in the cryoconite of glaciers on the Tibetan Plateau: abundance, speciation and implications

Abstract. Cryoconite is a mixture of impurities and ice visually represented by dark colors present in the ablation zone of glaciers. As an important constituent of light-absorbing impurities on the glacier surface, iron oxides influence the radiative properties of mineral dust and thus its impact on ice melting processes. In particular, the distinct optical properties between hematite and goethite (the major iron oxide species) highlight the necessity to obtain accurate knowledge about their abundance and geochemical behavior. Cryoconite samples from five glaciers in different regions of the Tibetan Plateau (TP) and surroundings were studied. The iron abundance in the cryoconite from TP glaciers ranged from 3.40 % to 4.90 % by mass, in accordance with typical natural background levels. Because the light absorption capacity of mineral dust essentially depends on the presence of iron oxides (i.e., free iron), iron oxides were extracted and determined using diffuse reflectance spectroscopy. The ratios of free to total iron for the five glaciers ranged from 0.31 to 0.70, emphasizing that iron in the form of oxides should be considered rather than total iron in the albedo and radiative modeling. Furthermore, the goethite content in iron oxides (in mass fraction) ranged from 81 % to 98 %, showing that goethite was the predominant form among the glaciers. Using the abundance and speciation of iron oxides as well as their optical properties, the total light absorption was quantitatively attributed to goethite, hematite, black carbon (BC) and organic matters at 450 and 600 nm wavelengths. We found that the goethite played a stronger role than BC at shorter wavelengths for most glaciers. Such findings were essential to understand the relative significance of anthropogenic and natural effects, and then taking the proper mitigation measures.

Mortality and emergency hospitalizations associated with atmospheric particulate matter episodes across the UK in spring 2014

Exposure to particulate air pollution is known to have negative impacts on human health. Long-term exposure to anthropogenic particulate matter is associated with the equivalent of around 29,000 deaths a year in the UK. However, short-lived air pollution episodes on the order of a few days are also associated with increased daily mortality and emergency hospital admissions for respiratory and cardiovascular conditions. The UK experienced widespread high levels of particulate air pollution in March–April 2014; observations of hourly mean PM2.5 concentrations reached up to 83μgm−3 at urban background sites. We performed an exposure and health impact assessment of the spring air pollution, focusing on two episodes with the highest concentrations of PM2.5 (12–14 March and 28 March–3 April 2014). Across these two episodes of elevated air pollution, totalling 10days, around 600 deaths were brought forward from short-term exposure to PM2.5, representing 3.9% of total all-cause (excluding external) mortality during these days. Using observed levels of PM2.5 from other years, we estimate that this is 2.0 to 2.7 times the mortality burden associated with typical urban background levels of PM2.5 at this time of year. Our results highlight the potential public health impacts and may aid planning for health care resources when such an episode is forecast.

Biomass burning emissions of trace gases and particles in marine air at Cape Grim, Tasmania

Abstract. Biomass burning (BB) plumes were measured at the Cape Grim Baseline Air Pollution Station during the 2006 Precursors to Particles campaign, when emissions from a fire on nearby Robbins Island impacted the station. Measurements made included non-methane organic compounds (NMOCs) (PTR-MS), particle number size distribution, condensation nuclei (CN) > 3 nm, black carbon (BC) concentration, cloud condensation nuclei (CCN) number, ozone (O3), methane (CH4), carbon monoxide (CO), hydrogen (H2), carbon dioxide (CO2), nitrous oxide (N2O), halocarbons and meteorology. During the first plume strike event (BB1), a 4 h enhancement of CO (max ~ 2100 ppb), BC (~ 1400 ng m-3) and particles > 3 nm (~ 13 000 cm-3) with dominant particle mode of 120 nm were observed overnight. A wind direction change lead to a dramatic reduction in BB tracers and a drop in the dominant particle mode to 50 nm. The dominant mode increased in size to 80 nm over 5 h in calm sunny conditions, accompanied by an increase in ozone. Due to an enhancement in BC but not CO during particle growth, the presence of BB emissions during this period could not be confirmed. The ability of particles > 80 nm (CN80) to act as CCN at 0.5 % supersaturation was investigated. The ΔCCN / ΔCN80 ratio was lowest during the fresh BB plume (56 ± 8 %), higher during the particle growth period (77 ± 4 %) and higher still (104 ± 3 %) in background marine air. Particle size distributions indicate that changes to particle chemical composition, rather than particle size, are driving these changes. Hourly average CCN during both BB events were between 2000 and 5000 CCN cm-3, which were enhanced above typical background levels by a factor of 6–34, highlighting the dramatic impact BB plumes can have on CCN number in clean marine regions. During the 29 h of the second plume strike event (BB2) CO, BC and a range of NMOCs including acetonitrile and hydrogen cyanide (HCN) were clearly enhanced and some enhancements in O3 were observed (ΔO3 / ΔCO 0.001–0.074). A short-lived increase in NMOCs by a factor of 10 corresponded with a large CO enhancement, an increase of the NMOC / CO emission ratio (ER) by a factor of 2–4 and a halving of the BC / CO ratio. Rainfall on Robbins Island was observed by radar during this period which likely resulted in a lower fire combustion efficiency, and higher emission of compounds associated with smouldering. This highlights the importance of relatively minor meteorological events on BB emission ratios. Emission factors (EFs) were derived for a range of trace gases, some never before reported for Australian fires, (including hydrogen, phenol and toluene) using the carbon mass balance method. This provides a unique set of EFs for Australian coastal heathland fires. Methyl halide EFs were higher than EFs reported from other studies in Australia and the Northern Hemisphere which is likely due to high halogen content in vegetation on Robbins Island. This work demonstrates the substantial impact that BB plumes can have on the composition of marine air, and the significant changes that can occur as the plume interacts with terrestrial, aged urban and marine emission sources.

Evaluation of a Closed Tunnel for Field‐Scale Measurements of Nitrous Oxide Fluxes from an Unfertilized Grassland Soil

Emissions of the major greenhouse gas NO from soils are characterized by huge spatial variability. An upscaling based on conventional small-scale chamber measurements is thus questionable and may involve a considerable amount of uncertainty. In this feasibility study, we evaluated the applicability of a large, closed tunnel for field-scale measurements of NO fluxes from an unfertilized grassland soil. The tunnel, coupled to an open-path Fourier transform infrared spectrometer, covered 500 m. During a 2-yr campaign, concurrent closed-chamber measurements (area of 0.045 m) were performed at the tunnel plot. The tunnel system enabled high-density and precise NO concentration measurements under dry, stable, nocturnal atmospheric conditions, but higher wind speeds and rain limited its application. To calculate an unbiased, predeployment NO flux from the increase of NO concentrations during tunnel deployment, we propose a novel approach based on inverse modeling (IMQ0). We show that IMQ0 is appropriate for the specific non-steady state tunnel setup. Compared with conventional models, which were developed for gas flux calculation from concentration gradients measured in vented closed chambers, IMQ0 is most accurate. Whereas NO fluxes obtained from the tunnel measurements were generally small and at a typical background level, the chamber measurements revealed high spatial and temporal variability of NO emissions, including slight NO uptake and precipitation-triggered emission peaks. The cumulative NO fluxes of both methods differed by one order of magnitude and were smaller for the tunnel measurements. We argue that the chambers were occasionally susceptible to detection of hotspots and hot moments of NO emission. However, these emissions were evidently not representative for the field scale. Compared with available greenhouse gas measurement techniques, we conclude that the tunnel may serve as a gap-filling method between small-scale chamber and ecosystem-level micrometeorological techniques, particularly during stable nocturnal conditions.

Assessment of daily exposure of endodontic personnel to extremely low frequency magnetic fields

To measure daily exposure levels to extremely low frequency magnetic fields (ELF MFs) in endodontic clinics. In total, 10 subjects (five endodontic trainees, five hygienists) participated. Each volunteer wore a 60-Hz MF measurement device on the left upper arm during working hours. Measurements were taken continuously throughout the working day except at lunch time. Separate measurements were taken for specific items of equipment at several distances. The average MF exposure for the 10 personnel was 0.03±0.04micro-Tesla (μT) (range, 0.01-6.4μT). The average MF exposure of endodontic personnel was lower than that of other hospital personnel according to the literature. Furthermore, all monitored exposure levels were well below the maximum acute exposure level, 500μT, recommended by the International Committee on Non-ionizing Radiation Protection for the protection of workers against ELF MFs. However, relatively high levels of exposure occurred in an operating room and X-ray room, presumably as a result of the use of surgical equipment such as microscopes and monitors, various motors and power cables of X-ray machines with large current flows. The total average MF exposure level of 0.03μT was lower than the typical background level at home. Although high levels of exposure were measured in an operating room and X-ray room, the MF exposure level to dental personnel was minimal during routine endodontic clinical work.

SERUM PERFLUORINATED COMPOUND CONCENTRATION AND ATTENTION DEFICIT/HYPERACTIVITY DISORDER IN CHILDREN AGED 5–18.

Background and Aims: Perfluorinated compounds (PFCs) are ubiquitous, environmental pollutants used to manufacture non-stick cookware and waterproof fabrics. Perfluorooctanoic acid (PFOA) and other PFCs are found in maternal and umbilical cord blood and breast milk. Toxicology studies demonstrate the potential for PFCs to impact human growth and development. Attention Deficit/Hyperactivity Disorder (ADD) is a developmental disorder with suspected environmental and genetic etiology. Objectives: We examined the cross-sectional association between serum PFC concentration and report of doctor-diagnosed ADD with and without current ADD medication use. Methods: We used data from the C8 Health Project, a 2005–2006 survey in a Mid-Ohio Valley community highly exposed to PFOA through contaminated drinking water, to examine the association between serum PFC concentration and report of doctor-diagnosed ADD in non-Hispanic white children aged 5–18. This community was highly exposed to PFOA, but exposure to other PFCs reflects typical background levels. Logistic regression models were adjusted for age and gender. Results: Of the 10,546 eligible children, 12.4% reported ADD, and 5.1% reported ADD plus current ADD medication use. The adjusted odds ratio (OR) for PFOA exposure above the 50th percentile was decreased (OR 0.80, 95% confidence interval (CI) 0.67, 0.95) for ADD plus medication as compared to exposure below the 50th percentile. Conversely, the OR for perfluorohexane sulfonic acid (PFHxS) levels above the 50th percentile was increased (OR 1.33, 95% CI 1.11, 1.59) for ADD plus medication as compared to exposure below the 50th percentile. There were no clear associations between the other PFCs and ADD. Conclusions: It seems unlikely that PFOA protects against ADD. We suspect that the inverse association between PFOA and ADD reflects a spurious finding related to the geographic determination of PFOA exposure in this population, or to unmeasured behavioral or physiologic correlates of both exposure and outcome.

The use of multivariate statistical analysis of geochemical data for assessing the spatial distribution of soil contamination by potentially toxic elements in the Aljustrel mining area (Iberian Pyrite Belt, Portugal)

Aljustrel mine is located in SW Portugal, in the western sector of the Iberian Pyrite Belt. The Aljustrel village was developed around the exploitations of massive polymetallic sulphides that occur in the area (4 orebodies mined, 2 in exploration phase). The pyrite ore was extensively exploited from 1850 to 1993, when production was discontinued. A mining restart occurred in 2008, only during a few months. The objectives of the study were to assess the levels of soil contamination, to determine associations between the different chemical elements and their spatial distribution, as well as to identify possible sources of contamination that can explain the spatial patterns of soil pollution in the area. Principal component analysis combined with spatial interpretation successfully grouped the elements according to their sources and provided evidence about their geogenic or anthropogenic origin. From this study, it is possible to conclude that soils around Algares/Feitais tailing deposits, Estéreis and Águas Claras mine dams and S. João mine show severe contamination. The highest concentrations of As (up to 3,936 mg kg−1) and certain heavy metals (up to 321.7 mg kg−1 for Bi, 5,414 mg kg−1 for Cu, 20,000 mg kg−1 for Pb, 980.6 mg kg−1 for Sb, and 22 mg kg−1 Cd) were obtained near Algares area while the highest concentration of Cd (up to 61.6 mg kg−1) and Zn (up to 20,000 mg kg−1) were registered in samples collected in the S. João area. The highest pollution load index (>4.0) was recorded at the Algares area where the metal concentrations exceed typical soil background levels by as much as two orders of magnitude.

Movement of a tritium plume in shallow groundwater at a legacy low-level radioactive waste disposal site in eastern Australia

Between 1960 and 1968 low-level radioactive waste was buried in a series of shallow trenches near the Lucas Heights facility, south of Sydney, Australia. Groundwater monitoring carried out since the mid 1970s indicates that with the exception of tritium, no radioactivity above typical background levels has been detected outside the immediate vicinity of the trenches. The maximum tritium level detected in groundwater was 390 kBq/L and the median value was 5400 Bq/L, decay corrected to the time of disposal. Since 1968, a plume of tritiated water has migrated from the disposal trenches and extends at least 100 m from the source area. Tritium in rainfall is negligible, however leachate from an adjacent landfill represents a significant additional tritium source. Study data indicate variation in concentration levels and plume distribution in response to wet and dry climatic periods and have been used to determine pathways for tritium migration through the subsurface.

Sediment response to catchment disturbances

1 IntroductionThe surface of the planet undergoes a constant battle forbalance between uplift and erosion. Plate tectonics causeland to be created and mountains to be born, whileweathering and erosion act to lower the land surface. Riverstransport the products of weathering and erosion to storagepoints, or sinks; the ultimate sink being the deep oceans. Fora given landscape, an equilibrium is reached whereby therates of sediment distribution between sources and sinks arefairly constant. In the case of a river channel, the amount ofwater and sediment moved through a landscape is balancedby the energy available to do this, such that a change ineither of the two generates adjustments in stream power. Achange in environmental conditions often results in aresponse, the magnitude of which is a function of the typeand intensity of “disturbance” to the system. In the case ofthe river channel, this might manifest itself in the form ofchannel aggradation or degradation, whereby sediments areeither deposited or eroded in response to changes in availableenergy or sediment supply.Changestoalandscapearebothnaturalandanthropogenic.In terms of landscapes, we tend to think of a “disturbance”eventasonethatisfairlyextremeandproducesameasureableresponse in the rate or type of processes occurring in thelandscape. Examples of natural disturbances include earth-quakes, volcanic activities and wildfires. Examples ofanthropogenic disturbances include deforestation, intensiveagriculture, urbanization, dam construction and gravel min-ing. Typically, in natural systems, the types of geomorphicresponses to these events include increased rates of sedimentmobilization (i.e., soil erosion, mass movements), transport(i.e., delivery to and within river channel systems) anddeposition (i.e., in floodplains, lakes, estuaries). A goodexample is the 1980 eruption of Mount St Helens volcano,USA, where annual suspended sediment yields after theeruption were as much as 500 times greater than typicalbackground levels. Even 20 years after the eruption, averagesuspendedsedimentyieldsfromthedebris-avalanchedepositsremained 100 times (10

Individual Particle Analysis of Atmospheric Aerosols at Nam Co, Tibetan Plateau

Twelve filter samples were sampled monthly during a continuous 1-year campaign at a remote site, Nam Co in central Tibetan Plateau. The total aerosol concentrations ranged from 0.48 μg/m3 to 36.11 μg/m3 with the annual average of 6.74 μg/m3, reflecting a typical background level. The composition and morphology of atmospheric aerosols with size ranging from 0.5 to 10 μm were investigated using a scanning electron microscope coupled with energy dispersive X-ray analysis. Then aerosol particles were classified into 7 groups: soot, tar ball, aluminosilicates/quartz, calcium sulfate, Ca/Mg carbonate, Fe/Ti oxide, and biological particle. Aerosol optical properties from the sun photometer and the results obtained by SEM-EDX could support and verify each other, providing complementary information on aerosol characteristics at Nam Co. Two distinct types of air masses arriving at Nam Co correspond to different aerosol constituent, showing that the summer monsoon circulation may bring considerable pollution from South Asia, while the westerly flow dominated in winter is relative clean.

Formaldehyde over North America and the North Atlantic during the summer 2004 INTEX campaign: Methods, observed distributions, and measurement‐model comparisons

A tunable diode laser absorption spectrometer (TDLAS) was operated on the NASA DC‐8 aircraft during the summer INTEX‐NA study to acquire ambient formaldehyde (CH2O) measurements over North America and the North Atlantic Ocean from ∼0.2 km to ∼12.5 km altitude spanning 17 science flights. Measurements of CH2O in the boundary layer and upper troposphere over the southeastern United States were anomalously low compared to studies in other years, and this was attributed to the record low temperatures over this region during the summer of 2004. Formaldehyde is primarily formed over the southeast from isoprene, and isoprene emissions are strongly temperature‐dependent. Despite this effect, the median upper tropospheric (UT) CH2O mixing ratio of 159 pptv from the TDLAS over continental North America is about a factor of 4 times higher than the median UT value of 40 pptv observed over remote regions during TRACE‐P. These observations together with the higher variability observed in this study all point to the fact that continental CH2O levels in the upper troposphere were significantly perturbed during the summer of 2004 relative to more typical background levels in the upper troposphere over more remote regions. The TDLAS measurements discussed in this paper are employed together with box model results in the companion paper by Fried et al. to further examine enhanced CH2O distributions in the upper troposphere due to convection. Measurements of CH2O on the DC‐8 were also acquired by a coil enzyme fluorometric system and compared with measurements from the TDLAS system.

Domestic radon remediation of U.K. dwellings by sub-slab depressurisation: Evidence for a baseline contribution from constructional materials

To quantify the effectiveness of Sub-Slab Depressurisation, widely used in the United Kingdom (U.K.) to mitigate indoor radon gas levels in residential properties, a study was made of radon concentration data collected from a set of 170 homes situated in Radon Affected Areas in Northamptonshire and neighbouring counties, remediated using conventional sump/pump technology. A high incidence of satisfactory remediation outcomes was achieved, with 100% of the houses remediated demonstrating post-remediation radon concentrations below the U.K. domestic Action Level of 200 Bq m−3, while more than 75% of the sample exhibited radon mitigation factors (defined as the ratio of radon concentrations following and prior to remediation) <0.2. Two systematic trends are identified. Firstly, absolute radon concentration reduction following remediation is directly proportional to initial radon concentration, with a mean reduction factor of 0.96 and a residual component of around 75 Bq m−3. Secondly, houses with lower initial radon concentrations demonstrate poorer (higher) mitigation factors. These observations support a model in which the total indoor radon concentration within a dwelling can be represented by two principal components, one susceptible to mitigation by sub-slab depressurisation, the other remaining essentially unaffected. The first component can be identified with radon emanating from the subsoil and bedrock geologies, percolating through the foundations of the dwelling as a component of the soil-gas, and potentially capable of being attenuated by sub-slab depressurisation or radon-barrier remediation technologies. The second contribution can be identified with radon emanating from materials used in the construction of the dwelling with a further contribution from the natural background level, and is essentially unaffected by ground-level remediation strategies. Modelling of a multi-component radon dependency using ground-radon attenuation factors derived from the experimental data, in conjunction with typical background and structural-radon levels, yields behaviour in good agreement with the observed dependence of mitigation factor on initial radon concentration.

Evaluation of Various Ammonia Assays for Testing of Contaminated Muscle Food Products

The indophenol method, ammonia ion selective electrode (ISE), Reflectoquant(R) test strips, and salicylate methods were evaluated to determine those that can be used for in-plant rapid testing of meat contaminated by ammonia refrigerant leaks. Ground eye of round beef samples were spiked with 25, 50, 100, or 200 ppm ammonia as (N) and the amounts recovered were corrected for typical background levels. The recovery of ammonia from spiked meat filtrates by ISE ranged from 98.3% to 100%+/- 2%, and the recovery of ammonia from spiked meat samples by ISE-perchloric acid method ranged from 90% to 110%+/- 8%. The measurement of ammonia in spiked meat samples by the Reflectoquant test strips ranged from 77.4% to 96.9%, but the standard deviation was higher than 14%. The recovery using the salicylate methods was less than 63% when meat samples were spiked with 25 or 50 ppm ammonia. Both indophenol and ammonia ISE are precise, give excellent recovery, and can be used for testing ammonia contamination in meat. Ammonia background levels of various commercial meat products was determined using the ammonia ISE and ranged from 87 to 166 ppm.

Fate of high loads of ammonia in a pond and wetland downstream from a hazardous waste disposal site

Halls Brook (eastern Massachusetts, USA) is a significant source of total dissolved ammonia (sum of NH(3) and NH(4)(+); (NH(3))(T)) to the Aberjona River, a water body listed for NH(3) impairment on the Clean Water Act section 303(d) list. We hypothesized (1) that (NH(3))(T) in Halls Brook derived from a hazardous waste site via groundwater discharging to a two-basin pond that feeds the brook; and (2) that transport of (NH(3))(T) to the Aberjona River was controlled by lacustrine and wetland processes. To test these hypotheses we measured (NH(3))(T) levels in the brook, the pond, and a wetlands directly downstream of the pond during both dry and wet weather over a ten month period. In addition, we analyzed sediment cores and nitrogen isotopes, and performed mass balance calculations. Groundwater discharge from beneath the hazardous waste site was the major source of (NH(3))(T) (20-67 kg d(-1)) and salinity to the north basin of the pond. The salty bottom waters of the north basin were anoxic on all sampling dates, and exhibited relatively stable (NH(3))(T) concentrations between 200 and 600 mg Nl(-1). These levels were >100-times higher than typical background levels, and 8-24-times above the acute effects level for (NH(3))(T) toxicity. Bottom waters from the north basin continuously spill over into the south basin contributing approximately 50% of the (NH(3))(T) load entering this basin. The remainder comes from Halls Brook, which receives (NH(3))(T) loadings from as yet unknown sources upstream. During storm events up to 50% of the mass of (NH(3))(T) was flushed from the south basin and into the wetlands. The wetlands acted as a (NH(3))(T) sink in dry weather in the growing season and a discharge-dependent (NH(3))(T) source to the Aberjona River during rainstorms.

Use of background inorganic arsenic exposures to provide perspective on risk assessment results

Background exposures provide perspective for interpreting calculated health risks associated with naturally occurring substances such as arsenic. Background inorganic arsenic intake from diet and water for children (ages 1–6 years) and all ages of the U.S. population was modeled stochastically using consumption data from USDA, published data on inorganic arsenic in foods, and EPA data on arsenic in drinking water. Mean and 90th percentile intakes for the U.S. population were 5.6 and 10.5 μg/day, assuming nationwide compliance with the 10 μg/L U.S. drinking water standard. Intakes for children were slightly lower (3.5 and 5.9 μg/day). Based on the current EPA cancer slope factor for arsenic, estimated lifetime risks associated with background diet and water at the mean and 90th percentile are 1 per 10,000 and 2 per 10,000, respectively. By comparison, reasonable maximum risks for arsenic in soil at 20 (higher typical background level) and 100 mg/kg are 4 per 100,000 and 2 per 10,000, using EPA default exposure assumptions. EPA reasonable maximum estimates of arsenic exposure from residential use of treated wood are likewise within background intakes. These examples provide context on how predicted risks compare to typical exposures within the U.S. population, thereby providing perspective for risk communication and regulatory decision-making on arsenic in the environment and in consumer products.