Municipal Compost Public Health, Waste Management, and Urban Agriculture: A Decadal Study of Fugitive Pb in City of Boston, Massachusetts, USA.

Compostable materials constitute roughly half of waste generated globally, but only 5% of waste is actually processed through composting, suggesting that expanding compost programs may be an effective way to process waste. Compostable waste, if properly collected and processed, has value-added end use options including: residential and park landscaping, remediation of brownfield sites, and as growing media in urban agriculture (UA). Since 2001, our lab has partnered with The Food Project, a non-profit focused on youth leadership development through urban farming. From 2006 to 2022 we collected compost materials that were delivered to the farm from a variety of local sources and analyzed a suite of biogeochemical properties including lead (Pb) concentrations, organic carbon, and grain size distribution. Pb concentrations of Boston's municipal compost always exceeded the current City of San Francisco soil and compost purchase standard (80 µg/g). In 2012 Boston's composting program was halted when it exceeded the 400 µg/g Environmental Protection Agency's Pb in soil benchmark. Urban Pb is geomobile and must be managed to minimize resuspension and transport of fines whose Pb concentration is often elevated compared to bulk compost. Consequently, urban farmers have to source lower Pb compost from suburban suppliers at significantly greater cost. Over a 15 year period and through several city vendor contracts, Pb concentrations in municipal compost remain at levels that warrant continued surveillance and risk assessment.

Lead (Pb) Bioaccessibility and Mobility Assessment of Urban Soils and Composts: Fingerprinting Sources and Refining Risks to Support Urban Agriculture.

While the presence of legacy lead (Pb) in urban soil is well documented, less is known about the bioaccessibility, transport, and exposure pathways of urban soil Pb. We study Pb bioaccessibility in Roxbury and Dorchester, MA, urban gardens to assess exposure risk and identify remediation strategies, applicable locally and in urban gardens across the country. We work in partnership with The Food Project, which brings the goals and perspectives of local farmers to the center of the research process and enables efficient local application of results to reduce Pb exposure. We measure changes in Pb bioaccessibility as a function of growing material, grain size, and Pb source. In comparison to soils, compost has lower total Pb concentrations, has lower Pb solubility in gastric fluid, and limits fine particle resuspension. The mean bioaccessible Pb concentration of compost is 265 mg/kg, nearly an order of magnitude lower than that of soils, and compost contains 14% higher carbon content than soils, which may account for the observed 19% lower Pb bioaccessibility in compost. For all matrices (soil, raised bed fill, and compost) grain sizes <37 µm contain a disproportionate fraction of the total pool of bioaccessible Pb. Furthermore, the isotopic composition of Pb in the size fractions linked with resuspension and elevated blood lead levels is indicative of leaded gasoline and leaded paint even decades removed from the primary deposition of these sources.

Sources and fates of heavy metals in a mining-impacted stream: temporal variability and the role of iron oxides.

Heavy metal contamination of surface waters at mining sites often involves complex interactions of multiple sources and varying biogeochemical conditions. We compared surface and subsurface metal loading from mine waste pile runoff and mine drainage discharge and characterized the influence of iron oxides on metal fate along a 0.9-km stretch of Tar Creek (Oklahoma, USA), which drains an abandoned Zn/Pb mining area. The importance of each source varied by metal; mine waste pile runoff contributed 70% of Cd, while mine drainage contributed 90% of Pb, and both sources contributed similarly to Zn loading. Subsurface inputs accounted for 40% of flow and 40-70% of metal loading along this stretch. Streambed iron oxide aggregate material contained highly elevated Zn (up to 27,000 µg g(-1)), Pb (up to 550 µg g(-1)) and Cd (up to 200 µg g(-1)) and was characterized as a heterogeneous mixture of iron oxides, fine-grain mine waste, and organic material. Sequential extractions confirmed preferential sequestration of Pb by iron oxides, as well as substantial concentrations of Zn and Cd in iron oxide fractions, with additional accumulation of Zn, Pb, and Cd during downstream transport. Comparisons with historical data show that while metal concentrations in mine drainage have decreased by more than an order of magnitude in recent decades, the chemical composition of mine waste pile runoff has remained relatively constant, indicating less attenuation and increased relative importance of pile runoff. These results highlight the importance of monitoring temporal changes at contaminated sites associated with evolving speciation and simultaneously addressing surface and subsurface contamination from both mine waste piles and mine drainage.

Increased incidence and altered risk demographics of childhood lead poisoning: predicting the impacts of the CDC's 5 µg/dL reference value in Massachusetts (USA).

In May 2012, the CDC adopted a new sliding scale reference value for childhood lead poisoning, reducing the former 10 µg/dL benchmark by half. Using Massachusetts (MA) as a model state, we estimated the change in the population of 9-47 month-olds at risk for lead poisoning. We then examined the impact of the 5 µg/dL reference value on the demographic characteristics of lead risk in MA communities. We find that the new CDC benchmark will lead to a 1470% increase in childhood lead poisoning cases among 9-47 month-olds in MA, with nearly 50% of the examined communities experiencing an increased prevalence of lead poisoning. Further, the top 10 MA communities with BLLs ≥5 µg/dL have significantly fewer foreign-born residents and significantly larger white populations than the highest risk communities formerly identified by the MA Childhood Lead Poisoning Prevention Program. The CDC's new 5 µg/dL lead poisoning benchmark will drastically increase the number of children with elevated BLLs and alter the distribution and demographics high-risk communities in MA.

Pig producer attitude towards surgical castration of piglets without anaesthesia versus alternative strategies.

A group of 160 Flemish pig farmers (n=160) were surveyed about their attitude towards surgical castration with anaesthesia (SCA) and without (SCN), immunocastration (IC), sperm sexing (SS) and the production of entire males (EM). The farmers' general preference was recorded as SCN>SS>SCA=IC>EM. The farmers' self-reported knowledge of the strategies was associated with their preference for SCA (negatively) and SS (positively). Herd size was correlated with farmers' preference for SCA (negatively) and SS (positively). Farmers perceived surgical castration without anaesthesia as the most favourable strategy in terms of farm profitability, animal performance and effectiveness against boar taint, but they expected the lowest consumer acceptance for this strategy. Surgical castration with anaesthesia was ranked the least favourable in terms of labour conditions. Production of entire males was viewed as the least profitable and the least effective strategy. Sperm sexing was positively perceived, particularly in terms of labour conditions, animal welfare, effectiveness and expected consumer acceptance. The farmers' opinion was quite homogeneous, especially regarding surgical castration without anaesthesia and production of entire males. Increasing our understanding of the farmers' perceptions will hopefully facilitate communication about this intricate issue.

Effect of amino acid level in the pig diet during growing and early finishing on growth response during the late finishing phase of lean meat type gilts.

BACKGROUND: This experiment examined the influence of different amino acid levels during the growing and early finishing diet and the late finishing diet on growth performance and carcass quality of a lean meat type gilt. In a two by two factorial trial, 96 gilts were divided over four treatments. The two factors were (1) amino acid level in growing and early finishing and (2) amino acid level in late finishing. For the low amino acid diets we lowered the lysine, methionine, threonine and tryptophan levels by 20% and 30% in the growing and two finishing phases, respectively. RESULTS: Restricting amino acid levels in growing and early finishing led to a decreased growth rate but improved efficiency of amino acid use, which lasted into the subsequent phase. Pigs on a high amino acid diet in late finishing pigs were able to compensate to a large extent for amino acid restriction in growing and early finishing. Amino acid content in late finishing determined carcass quality. CONCLUSION: In the lean meat type gilts used in this experiment, restricting amino acid concentrations by 20% in the growing and 30% in the early finishing phase increased the growth rate and efficiency of growth in the subsequent late finishing phase. In order to obtain good carcass quality, it is crucial to provide the animals with a balanced diet during the late finishing phase.

Considerations on the performance of immunocastrated male pigs.

With the ongoing social pressure on surgical castration of pigs, an increase in the population of pigs that are either not castrated or immunocastrated (IC) can be expected. In both cases, their nutrient requirements and performance will differ from surgically castrated pigs and will require changes in their management. Immunocastration is performed by giving two injections of a modified gonadotrophin-releasing hormone component along with an adjuvant, at least 4 weeks apart. This paper describes the reported differences in growth performance and carcass quality of IC male pigs in comparison with boars (BO) and barrows (BA). Theoretically, IC pigs remain physiologically boar until the second vaccination and therefore, growth may be comparable with BO until this second vaccination. From then on, IC male pigs consume more feed than BO and grow faster when fed ad libitum. IC showed a faster growth and better feed conversion ratio than BA. When fed restrictedly, BO grow faster and more efficiently than BA and IC. IC have a lower carcass yield than BA and BO, whereas meat percentage is intermediate.

Reducing nitrogen excretion and soybean meal use by feeding a lower rumen degradable protein balance and protected soybean meal to dairy cattle.

To reduce N pollution by dairy cows, two levels of rumen degradable protein balance (RDPB) and the use of protected protein sources were studied in two feeding trials. Trial 1 investigated if the effect of lowering the RDPB, at a constant DPI (digestible protein in the intestine) supply, could be compensated by using protected protein sources (formaldehyde treated (= formolated) soybean meal (FSBM) or a combination of FSBM and formolated rapeseed meal at a ratio of 60:40). Trial 2 studied if FSBM is as effective as soybean meal (SBM) at a low RDPB level. Each trial was set up as a Latin square design, with three treatments and three periods, involving 18 lactating Holstein cows. Reducing RDPB from about 150 g/d to below -40 g/d resulted in small negative effects on the milk production, independent of the protein source (protected or not). However, N excretion per kg fat and protein corrected milk (FPCM) and N efficiency were both improved. At a low RDPB level, the performance of FSBM (35.0 kg FPCM) was no better than after feeding a combination of FSBM and formolated rapeseed meal (34.7 kg FPCM). The use of FSBM (32.8 kg FPCM and 34.2% N efficiency) was as effective as SBM (32.5 kg FPCM and 34.2% N efficiency). As such, SBM use can approximately be halved by using FSBM, possibly in combination with locally produced rapeseed meal.

Effect of decreasing ideal protein levels on performance results and nitrogen efficiency of growing-finishing gilts.

This study examined the effect of decreasing ideal protein concentrations on performance and nutrient efficiency. The experimental diets contained 100%, 90%, 80% or 70% of the ideal dietary protein level (Diet 100%, 90%, 80% and 70%, respectively) estimated in previous experiments with pigs of the same genetic background. The four different treatments were divided among 16 pens of six pigs each. The average initial and final body weight were 20.8 +/- 1.1 and 107 +/- 3 kg, respectively. Three-phase feeding was applied (BW 20-40 kg, 40-70 kg and 70-110 kg). The dietary ileal digestible (ID) methionine + cystine, threonine, tryptophan, isoleucine, valine, and leucine contents expressed as percent of ID lysine were 63, 72, 22, 60, 68, and > 100%, respectively. The lysine to protein ratio was kept constant at 6.8%. Between 21 and 106 kg BW the best performance was achieved on Diet 90%. Diet 70% led to significantly worse results. Although lean meat percentage did not differ, protein content of the carcass was lower on Diet 70% than on Diets 90% and 100%. Decreased protein concentrations increased crude protein efficiency and consequently decreased nitrogen excretion most at the 80% level. If protein varies together with digestible amino acid content, it can be concluded that Diet 80% may be the best choice for the environment and for profitability. If protein content stays at a fixed level, Diet 90% may be the safest choice.

Pediatric lead exposure from imported Indian spices and cultural powders.

BACKGROUND: Significant lead poisoning has been associated with imported nonpaint products. OBJECTIVES: To describe cases of pediatric lead intoxication from imported Indian spices and cultural powders, determine lead concentrations in these products, and predict effects of ingestion on pediatric blood lead levels (BLLs). PATIENTS AND METHODS: Cases and case-study information were obtained from patients followed by the Pediatric Environmental Health Center (Children's Hospital Boston). Imported spices (n = 86) and cultural powders (n = 71) were analyzed for lead by using x-ray fluorescence spectroscopy. The simple bioaccessibility extraction test was used to estimate oral bioavailability. The integrated exposure uptake biokinetic model for lead in children was used to predict population-wide geometric mean BLLs and the probability of elevated BLLs (>10 microg/dL). RESULTS: Four cases of pediatric lead poisoning from Indian spices or cultural powders are described. Twenty-two of 86 spices and foodstuff products contained >1 microg/g lead (for these 22 samples, mean: 2.6 microg/g [95% confidence interval: 1.9-3.3]; maximum: 7.6 microg/g). Forty-six of 71 cultural products contained >1 microg/g lead (for 43 of these samples, mean: 8.0 microg/g [95% confidence interval: 5.2-10.8]; maximum: 41.4 microg/g). Three sindoor products contained >47% lead. With a fixed ingestion of 5 microg/day and 50% bioavailability, predicted geometric mean BLLs for children aged 0 to 4 years increased from 3.2 to 4.1 microg/dL, and predicted prevalence of children with a BLL of >10 microg/dL increased more than threefold (0.8%-2.8%). CONCLUSIONS: Chronic exposure to spices and cultural powders may cause elevated BLLs. A majority of cultural products contained >1 microg/g lead, and some sindoor contained extremely high bioaccessible lead levels. Clinicians should routinely screen for exposure to these products.

Feeding measures to reduce nitrogen excretion in dairy cattle.

Feeding measures with a potential to improve N efficiency in dairy cattle husbandry were studied at two levels of undegradable protein balance (OEB). In each of the two experiments, two simultaneous Latin squares were conducted, each with three treatments and three lactating Holstein cows. Decreasing the OEB of the diet improved N efficiency and resulted in lower N excretion per kg milk. To avoid a negative effect of the decreased OEB on the production results, spreading the concentrate intake (as TMR or in five meals) seemed to be most promising, although only few significant effects were found. The use of protected protein sources or the addition of clinoptilolite were not successful in improving N-efficiency. The rather well balanced mixed basal diet and the large variation between animals seem to have hampered the assessment of such significant influences.

Response of 40-70 kg barrows and gilts to increasing ideal protein concentrations in the diet.

In Belgium, crossing a hybrid dam with a Piétrain sire leads to a rather lean and meaty fattening pig type. A digestibility trial and a performance trial were carried out to determine protein needs of this pig type. Six experimental diets with increasing protein content were formulated with 0.65-1.25% apparent ileal digestible lysine. The feeds were formulated to the ideal protein composition, with lysine as the reference amino acid. Standardised and apparent digestible amino acid values of the extreme diets were measured in a digestibility trial with four gilts cannulated at the end of the ileum, with an average initial and final BW of 39.1 kg and 55.3 kg, respectively, using a protein-free feed to estimate the basal endogenous N-losses. A performance trial at 13-18 weeks of age (40-70 kg BW) was performed with barrows and gilts separately at six protein levels, balanced in lysine, threonine, methionine and tryptophan. The experiment consisted of 11 pens (of 5 animals) per treatment and per sex. Average daily gain (ADG) and feed conversion ratio (FCR) reached maximal performance within the experimental lysine range for both sexes. Based on the ADG-data for barrows and on the ADG- and FCR-data for gilts, a protein level for optimal performance corresponded with a standardised ileal digestible lysine concentration of 0.89% for barrows and of 1.07-1.09% for gilts.

Urban gardens: lead exposure, recontamination mechanisms, and implications for remediation design.

Environmental lead contamination is prevalent in urban areas where soil represents a significant sink and pathway of exposure. This study characterizes the speciation of lead that is relevant to local recontamination and to human exposure in the backyard gardens of Roxbury and Dorchester, MA, USA. One hundred forty-one backyard gardens were tested by X-ray fluorescence, and 81% of gardens have lead levels above the US EPA action limit of 400 microg/g. Raised gardening beds are the in situ exposure reduction method used in the communities to promote urban gardening. Raised beds were tested for lead and the results showed that the lead concentration increased from an initial range of 150+/-40 microg/g to an average of 336 microg/g over 4 years. The percent distribution of lead in the fine grain soil (<100 microm) and the trace metal signature of the raised beds support the conclusion that the mechanism of recontamination is wind-transported particles. Scanning electron microscopy and sequential extraction were used to characterize the speciation of lead, and the trace metal signature of the fine grain soil in both gardens and raised gardening beds is characteristic of lead-based paint. This study demonstrates that raised beds are a limited exposure reduction method and require maintenance to achieve exposure reduction goals. An exposure model was developed based on a suite of parameters that combine relevant values from the literature with site-specific quantification of exposure pathways. This model suggests that consumption of homegrown produce accounts for only 3% of children's daily exposure of lead while ingestion of fine grained soil (<100 microm) accounts for 82% of the daily exposure. This study indicates that urban lead remediation on a yard-by-yard scale requires constant maintenance and that remediation may need to occur on a neighborhood-wide scale.

Effect of seven hours intermittent suckling and flavour recognition on piglet performance.

A low feed intake during the first days after weaning is predisposing for weaning diarrhoea and weight loss. In this experiment we tried to increase the feed intake of the piglets after weaning by stimulating the solid feed intake during the last two weeks before weaning by separating them from the sows for 7 h/d. In addition, the effect of flavour recognition and the interaction of flavour recognition with intermittent suckling were tested. In two consecutive weaning rounds, sows were divided over two compartments with 7 to 10 sows each. They were assigned to one of four treatments in a two factorial design: control housing/control feed (n = 7); control housing/ flavoured feed (n = 8); intermittent suckling/control feed (n = 7); intermittent suckling/ flavoured feed (n = 9). After weaning, for each round 3 pens of 6 pigs were selected per treatment group. All these piglets received the same feed with the same flavour at the same concentration. Contrary to the expectations, intermittent suckling decreased the solid feed intake during the last two weeks before weaning. Flavour addition to the creep feed did not increase feed intake or other performance parameters before and after weaning, nor did it interact with intermittent suckling. Although after intermittent suckling pigs ate less creep feed before weaning, they did not perform worse after weaning. However, to increase feed intake after weaning, longer periods of separation might be necessary.

Dendrochemical record of historical lead contamination sources, Wells G&H Superfund site, Woburn, Massachusetts.

Laser-ablation inductively coupled-plasma mass-spectrometry analysis of red oak (Quercus rubra) from a well documented heavy metal contaminated United States Environmental Protection Agency superfund site in Woburn, Massachusetts reveals decade-long trends in Pb contaminant sources. Lead isotope ratios (207Pb/206Pb and 208Pb/206Pb) in tree rings plot along a linear trend bracketed by several local and regional contamination sources. Statistically significant interannual variations in 207Pb/206Pb suggest that atmospheric Pb is rapidly incorporated into wood, with minimal mobility subsequent to deposition in annual growth rings. We interpret the decadal trends in our record as a changing mixture of local pollution sources and gasoline-derived Pb. Between 1940 and 1970, Pb was predominantly derived from remobilization of local industrial Pb sources. An abrupt shift in 207Pb/206Pb may indicate that local Pb sources were overwhelmed by gasoline-derived Pb during the peak of leaded gasoline emissions in the late 1960s and early 1970s.

Characterization of zinc, lead, and cadmium in mine waste: implications for transport, exposure, and bioavailability.

We characterized the lability and bioaccessibility of Zn, Pb, and Cd in size-fractionated mine waste at the Tar Creek Superfund Site (Oklahoma) to assess the potential for metal transport, exposure, and subsequent bioavailability. Bulk mine waste samples contained elevated Zn (9100 +/- 2500 ppm), Pb (650 +/- 360 ppm), and Cd (42 +/- 10 ppm), while particles with the greatest potential for windborne transport and inhalation (< 10 microm) contained substantially higher concentrations, up to 220 000 ppm Zn, 16 000 ppm Pb, and 530 ppm Cd in particles < 1 microm. Although the mined ore at Tar Creek primarily consisted of refractory metal sulfides with low bioavailability, sequential extractions and physiologically based extractions indicate that physical and chemical weathering have shifted metals into relatively labile and bioaccessible mineral phases. In < 37 microm mine waste particles, 50-65% of Zn, Pb, and Cd were present in the "exchangeable" and "carbonate" sequential extraction fractions, and 60-80% of Zn, Pb, and Cd were mobilized in synthetic gastric fluid, while ZnS and PbS exhibited minimal solubility in these solutions. Our results demonstrate the importance of site-specific characterization of size-fractionated contemporary mine waste when assessing the lability and bioavailability of metals at mine-waste impacted sites.

Sources, sinks, and exposure pathways of lead in urban garden soil.

The chemistry of Pb in urban soil must be understood in order to limit human exposure to Pb in soil and produce and to implement remediation schemes. In inner-city gardens where Pb contamination is prevalent and financial resources are limited, it is critical to identify the variables that control Pb bioavailability. Field-portable X-ray fluorescence was used to measure Pb in 103 urban gardens in Roxbury and Dorchester, MA, and 88% were found to contain Pb above the USEPA reportable limit of 400 mug g(-1). Phosphorus, iron, loss on ignition, and pH data were collected, Pb-bearing phases were identified by X-ray diffraction, and Pb isotopes were measured using inductively coupled plasma mass spectrometry. Four test crops were grown both in situ and in Roxbury soil in a greenhouse, and plant tissue was analyzed for Pb uptake by polarized energy-dispersive X-ray fluorescence. Variation at the neighborhood scale in soil mineralogical and chemical characteristics suggests that the bioavailable fraction of Pb in gardens is site specific. Based on Pb isotope analysis, two historical Pb sources appear to dominate the inventory of Pb in Roxbury gardens: leaded gasoline ((207) Pb/(206) Pb = 0.827) and Pb-based paint ((207)Pb/(206) Pb = 0.867). Nearly 70% of the samples analyzed can be isotopically described by mixing these two end members, with Pb-based paint contributing 40 to 80% of the mass balance. A simplified urban human exposure model suggests that the consumption of produce from urban gardens is equivalent to approximately 10 to 25% of children's daily exposure from tap water. Furthermore, analysis of over 60 samples of plant tissue from the four test species suggests that in these urban gardens unamended phytoremediation is an inadequate tool for decreasing soil Pb.

Effect of daily concentrate intake at weaning on performance of Belgian Blue double-muscled rearing calves.

Weaning at a different daily concentrate intake was investigated during a 140-d experimental period, using 54 male and 68 female newborn Belgian Blue double-muscled animals. They were divided into three comparable groups and received milk at 10% of their birth weight up to weaning. Concentrate was levelled off at a maximum daily intake of 3 kg, while grass hay was freely available. Weaning occurred at a daily concentrate intake level (CL) of 0.5, 0.75 and 1.0 kg, respectively. Weaning at an increased CL prolonged the milk-feeding period by 13.1 and 14.6 days, and resulted in a higher pre- and post-weaning growth rate (p < 0.05). Daily gain during the entire experimental period averaged 0.84, 0.85 and 0.88 kg for the respective groups (p = 0.065). Daily concentrate intake was not different among groups, with only a small effect of CL on intake around weaning. Early weaning resulted in a significant reduction of hay intake (p = 0.032). Total daily net energy intake increased slightly with a higher CL at weaning, so that energy conversion was slightly improved, amounting to 17.7, 17.6 and 17.4 MJ/kg gain, respectively. Energy balance during the first week after weaning was negative for CL 0.5 kg (-22%), while it was close to 0 for CL 0.75 kg (-2%) or positive for CL 1.0 kg. Most effects of CL at weaning were similar for males and females, but male calves tended to have a higher intake and a faster growth rate than females. It can be concluded that weaning should be delayed until Belgian Blue double-muscled calves consume at least 0.75 kg per day or more for reasons of welfare, although performance was hardly improved by weaning at a daily concentrate intake of more than 0.5 kg per day.

Arsenic sequestration by ferric iron plaque on cattail roots.

Typha latifolia (cattail) sequesters arsenic within predominantlyferric iron root coatings, thus decreasing mobility of this toxic element in wetland sediments. Element-specific XRF microtomographic imaging illustrated a high spatial correlation between iron and arsenic in root plaques, with little arsenic in the interior of the roots. XANES analyses demonstrated that the plaque was predominantly ferric iron and contained approximately 20% As(III) and 80% As(V), which is significant because the two oxidation states form species that differ in toxicity and mobility. For the first time, spatial distribution maps of As oxidation states were developed, indicating that As(III) and As(V) are both fairly heterogeneous throughoutthe plaque. Chemical extractions showed that As was strongly adsorbed in the plaque rather than coprecipitated. Iron and arsenic concentrations ranged from 0.03 to 0.8 g Fe g(-1) wet plaque and 30 to 1200 microg As g(-1) wet plaque, consistent with a mechanism of As adsorption onto Fe(III) oxyhydroxide plaque. Because this mechanism decreases the concentrations of both As(III) and As(V) in groundwater, we propose that disruption of vegetation could increase the concentrations of mobile arsenic.

Arsenic mobility and groundwater extraction in Bangladesh.

High levels of arsenic in well water are causing widespread poisoning in Bangladesh. In a typical aquifer in southern Bangladesh, chemical data imply that arsenic mobilization is associated with recent inflow of carbon. High concentrations of radiocarbon-young methane indicate that young carbon has driven recent biogeochemical processes, and irrigation pumping is sufficient to have drawn water to the depth where dissolved arsenic is at a maximum. The results of field injection of molasses, nitrate, and low-arsenic water show that organic carbon or its degradation products may quickly mobilize arsenic, oxidants may lower arsenic concentrations, and sorption of arsenic is limited by saturation of aquifer materials.