A modified risk assessment to establish molybdenum standards for land application of biosolids

The USEPA standards (40 CFR Part 503) for the use or disposal of sewage sludge (biosolids) derived risk-based numerical values for Mo for the biosolids --> land --> plant --> animal pathway (Pathway 6). Following legal challenge, most Mo numerical standards were withdrawn, pending additional field-generated data using modern biosolids (Mo concentrations <75 mg kg(-1) and a reassessment of this pathway. This paper presents a reevaluation of biosolids Mo data, refinement of the risk assessment algorithms, and a reassessment of Mo-induced hypocuprosis from land application of biosolids. Forage Mo uptake coefficients (UC) are derived from field studies, many of which used modern biosolids applied to numerous soil types, with varying soil pH values, and supporting various crops. Typical cattle diet scenarios are used to calculate a diet-weighted UC value that realistically represents forage Mo exposure to cattle. Recent biosolids use data are employed to estimate the fraction of animal forage (FC) likely to be affected by biosolids applications nationally. Field data are used to estimate long-term Mo leaching and a leaching correction factor (LC) is used to adjust cumulative biosolids application limits. The modified UC and new FC and LC factors are used in a new algorithm to calculate biosolids Mo Pathway 6 risk. The resulting numerical standards for Mo are cumulative limit (RPc)=40 kg Mo ha(-1), and alternate pollutant limit (APL) = 40 mg Mo kg(-1) We regard the modifications to algorithms and parameters and calculations as conservative, and believe that the risk of Mo-induced hypocuprosis from biosolids Mo is small. Providing adequate Cu mineral supplements, standard procedure in proper herd management, would augment the conservatism of the new risk assessment.     

Bioavailability of biosolids molybdenum to soybean grain

Legumes grown in biosolids-amended soils and then fed to ruminants can represent problematic sources of molybdenum (Mo), but few field data are available to quantify the risk. We used a set of fields amended to high cumulative biosolids Mo loads (>18 kg ha(-1)) over 27 yr to generate additional data. Soybean [Glycine max (L.) Merr.] was grown on 29 fields (pH values>6.8) amended to a wide range of soil Mo loads. Soybean grain harvested from each field was analyzed for Mo and the concentrations regressed against soil Mo loads estimated from actual soil Mo concentrations in the 0- to 15-cm depth. Slopes of such linear regressions represent uptake coefficients (UC values) used by the USEPA to assess risk of biosolids Mo to ruminants fed forage grown on biosolids-amended land. The UC value for all 29 fields was estimated as 1.66, which agrees with the few soybean grain data in the literature. The UC value, however, is well below a conservative UC value of 4, recently recommended for all fresh legume materials fed to cattle. Soybean grain can contain high concentrations of Mo (>10 mg kg(-1)) and have low (<2:1) Cu to Mo ratios, which can exacerbate molybdenosis problems in cattle. However, soybean grain normally constitutes only -10% of dairy cattle diet, and other constituents (e.g., corn grain, stover, mineral supplements) are sufficient, or can be manipulated, to control molybdenosis.     

Bioavailability of biosolids molybdenum to corn

This study was part of a larger effort to generate field data appropriate to the assessment of biosolids molybdenum (Mo) risk to ruminants. Corn (Zea mays L.) is an important component of cattle diet, and is a logical crop for biosolids amendment owing to its high N requirement. Paired soil and corn stover samples archived from two unique field experiments were analyzed to quantify the relationship (uptake coefficient, UC) between stover Mo and soil Mo load. Both studies used biosolids with total Mo concentrations typical of modern materials. Data from long-term (continuous corn) plots in Fulton County, IL confirm expected low Mo accumulation by corn stover, even at very high biosolids loads and soil Mo loads estimated to be near 18 kg Mo ha(-1). Uptake slopes were actually negative, but USEPA protocol would assign UC values of 0.001. Data from plots in Minnesota also suggested essentially no correlations between stover Mo and soil Mo loads for continuous corn. However, greater Mo accumulation in corn grown following soybean [Glycine max (L.) Merr.] suggests the possibility of enhanced Mo bioavailability to corn in corn-soybean rotations. Nevertheless, molybdenosis risk to cattle consuming corn stover produced on biosolids-amended land is small as stover Mo concentrations were always low and stover Cu to Mo ratios exceeded 2:1, which avoids molybdenosis problems.     

Long-term biosolids application effects on metal concentrations in soil and bermudagrass forage

The long-term application of biosolids that periodically contained elevated metal concentrations has raised questions about potential effects on animal health. To address these concerns, we determined metal concentrations (As, Cd, Cu, Pb, Hg, Mo, Ni, Se, and Zn) in both soil and bermudagrass [Cynodon dactylon (L.) Pers.] forage from 10 fields in the following categories of biosolids application: six or more years (>6YR), less than six years (<6YR), and no applications (NS). Soil metal concentrations in all groups were similar to values reported for mineral soils in Georgia, and well below USEPA cumulative limits. Average metal concentrations in the forage were below the maximum tolerable level (MTL) for beef cattle, although two biosolids-amended fields in the >6YR group produced forage that was at or near the MTL for Cd and Mo, and one field in the <6YR group produced forage above the MTL for Cd. The Cu to Mo ratios in forage decreased with increasing time of sludge application, with the average in the >6YR group at a proposed 5:1 Cu to Mo ratio limit to protect ruminant health. Sulfur concentrations in the forage from all three groups was near the MTL of 4 g kg(-1). The study indicated that toxic levels of metals have not accumulated in the soils due to long-term biosolids application. Overall forage quality from the biosolids-amended fields was similar to that of commercially fertilized fields; however, due to the relatively high S and potential for a low Cu to Mo ratio, Cu supplements should be used to ensure ruminant health.     

Infrequent composted biosolids applications affect semi-arid grassland soils and vegetation

Monitoring of repeated composted biosolids applications is necessary for improving beneficial reuse program management strategies, because materials will likely be reapplied to the same site at a future point in time. A field trial evaluated a single and a repeated composted biosolids application in terms of long-term (13–14 years) and short-term (2–3 years) effects, respectively, on soil chemistry and plant community in a Colorado semi-arid grassland. Six composted biosolids rates (0, 2.5, 5, 10, 21, 30 Mg ha^?1) were surface applied in a split-plot design study with treatment (increasing compost rates) as the main factor and co-application time (1991, or 1991 and 2002) as the split factor applications. Short- and long-term treatment effects were evident in 2004 and 2005 for soil 0–8 cm depth pH, EC, NO₃-N, NH₄-N, total N, and AB-DTPA soil Cd, Cu, Mo, Zn, P, and Ba. Soil organic matter increases were still evident 13 and 14 years following composted biosolids application. The repeated composted biosolids application increased soil NO₃-N and NH₄-N and decreased AB-DTPA extractable Ba as compared to the single composted biosolids application in 2004; differences between short- and long-term applications were less evident in 2005. Increasing biosolids rates resulted in increased native perennial grass cover in 2005. Plant tissue Cu, Mo, Zn, and P concentrations increased, while Ba content decreased depending on specific plant species and year. Overall, the lack of many significant negative effects suggests that short- or long-term composted biosolids application at the rates studied did not adversely affect this semi-arid grassland ecosystem.     

ENVIRONMENTAL IMPACTS OF APPLYING MANURE,FERTILIZER, AND SEWAGE BIOSOLIDS ON A DAIRY FARM1

ABSTRACT: Farms that once spread only manures are now also applying sewage biosolids (sludge) and/or other wastes such as those from food processing. The objective of this study was to monitor environmental impacts at a dairy farm applying these materials. Fields were selected representing recent waste applications of manure (M1, M2), sewage biosolids (B1, B2), or fertilizer only control (F1, F2), although most fields had historical biosolids applications. Fields representing each treatment were not experimental replicates because of varying applications and soil characteristics. Septage and food processing wastes were also applied. Soil percolates were collected with wick lysimeters. Runoff was sampled at seven stream sites. Test field soils and alfalfa (Medicago sativa) were analyzed for trace elements. Cumulative trace metal loadings were low, at most only 1 percent of USEPA Part 503 limits. Surface soil enrichment was most evident for Mo, P, and S. Alfalfa tissue showed no trends of concern. The B2 site had the greatest percolate concentrations for 6 of 13 elements. Percolate Cu was somewhat elevated at Sites M1, M2, B2, and Fl. Percolate sodium was elevated on all M and B fields and sulfur was greatest at M2, B1, and B2. Soluble orthophosphate correlated with stream discharge during intensive monitoring of Stream Sites S1 (fertilizer) and S2 (biosolids). Peaks in S2 streamwater Mo lagged large runoff events by five days. Total streamwater export of Cu, Na, Mo, and soluble P were greater from the S2 biosolids subwatershed than from the S1 fertilizer subwatershed. Percolate concentrations exceeded corresponding streamwater concentrations in most cases.     

On-farm assessment of biosolids effects on soil and crop tissue quality

Agronomic use of biosolids as a fertilizer material remains controversial in part due to public concerns regarding the potential pollution of soils, crop tissue, and ground water by excess nutrients and trace elements in biosolids. This study was designed to assess the effects of long-term commercial-scale application of biosolids on soils and crop tissue sampled from 18 production farms throughout Pennsylvania. Biosolids application rates ranged from 5 to 159 Mg ha(-1) on a dry weight basis. Soil cores and crop tissue samples from corn (Zea mays L.), soybean (Glycine spp.), alfalfa (Medicago sativa L.), orchardgrass (Dactylis spp.) hay, and/or sorghum [Sorghum bicolor (L.) Moench] were collected for three years from georeferenced locations at each farm. Samples were tested for nutrients, trace elements, and other variables. Biosolids-treated fields had more post-growing season soil NO3 and Ca and less soil K than control fields and there was some evidence that soil P concentrations were higher in treated fields. The soil concentrations of Cu, Cr, Hg, Mo, Mn, Pb, and Zn were higher in biosolids-treated fields than in control fields; however, differences were < or = 0.06 of the USEPA Part 503 cumulative pollutant loading rates (CPLRs). There were no differences in the concentrations of measured nutrients or trace elements in the crop tissue grown on treated or control fields at any time during the study. Commercial-scale biosolids application resulted in soil trace element increases that were in line with expected increases based on estimated trace element loading. Excess NO3 and apparent P buildup indicates a need to reassess biosolids nutrient management practices.     

Phosphorus forms in biosolids-amended soils and losses in runoff: effects of wastewater treatment process

Continuous addition of municipal biosolids to soils based on plant nitrogen (N) requirements can cause buildup of soil phosphorus (P) in excess of crop requirements; runoff from these soils can potentially contribute to nonpoint P pollution of surface waters. However, because biosolids are often produced using lime and/or metal salts, the potential for biosolids P to cause runoff P losses can vary with wastewater treatment plant (WWTP) process. This study was conducted to determine the effect of wastewater treatment process on the forms and amounts of P in biosolids, biosolids-amended soils, and in runoff from biosolids-amended soils. We amended two soil types with eight biosolids and a poultry litter (PL) at equal rates of total P (200 kg ha(-1); unamended soils were used as controls. All biosolids and amended soils were analyzed for various types of extractable P, inorganic P fractions, and the degree of P saturation (acid ammonium oxalate method). Amended soils were placed under a simulated rainfall and all runoff was collected and analyzed for dissolved reactive phosphorus (DRP), iron-oxide-coated filter paper strip-extractable phosphorus (FeO-P), and total phosphorus (EPA3050 P). Results showed that biosolids produced with a biological nutrient removal (BNR) process caused the highest increases in extractable soil P and runoff DRP. Alternatively, biosolids produced with iron only consistently had the lowest extractable P and caused the lowest increases in extractable soil P and runoff DRP when added to soils. Differences in soil and biosolids extractable P levels as well as P runoff losses were related to the inorganic P forms of the biosolids.     

Biosolids affect soil barium in a dryland wheat agroecosystem

In December 2003, the USEPA released an amended list of 15 "candidate pollutants for exposure and hazard screening" with regard to biosolids land application, including Ba. Therefore, we decided to monitor soil Ba concentrations from a dryland wheat (Triticum aestivum L.)-fallow agroecosystem experiment. This experiment received 10 biennial biosolids applications (1982-2003) at rates from 0 to 26.8 dry Mg ha(-1) per application year. The study was conducted on a Platner loam (Aridic Paleustoll), approximately 30 km east of Brighton, CO. Total soil Ba, as measured by 4 M HNO(3), increased with increasing biosolids application rate. In the soil-extraction data from 1988 to 2003, however, we observed significant (P < 0.10) linear or exponential declines in ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA) extractable Ba concentrations as a function of increasing biosolids application rates. This was observed in 6 of 7 and 3 of 7 yr for the 0- to 20- and 20- to 60-cm soil depths, respectively. Results suggest that while total soil Ba increased as a result of biosolids application with time, the mineral form of Ba was present in forms not extractable with AB-DTPA. Scanning electron microscopy using energy dispersive spectroscopy verified soil Ba-S compounds in the soil surface, probably BaSO(4). Wet chemistry sequential extraction suggested BaCO(3) precipitation was increasing in the soil subsurface. Our research showed that biosolids application may increase total soil Ba, but soil Ba precipitates are insoluble and should not be an environmental concern in similar soils under similar climatic and management conditions.     

Herbaceous vegetation productivity, persistence, and metals uptake on a biosolids-amended mine soil

The selection of plant species is critical for the successful establishment and long-term maintenance of vegetation on reclaimed surface mined soils. A study was conducted to assess the capability of 16 forage grass and legume species in monocultures and mixes to establish and thrive on a reclaimed Appalachian surface mine amended with biosolids. The 0.15-ha coarse-textured, rocky, non-acid forming mined site was prepared for planting by grading to a 2% slope and amending sandstone overburden materials with a mixture of composted and dewatered, anaerobically digested biosolids at a rate of 368 Mg ha(-1) (dry weight). Tall fescue (Festuca arundinacea Schreb.), orchardgrass (Dactylis glomerata L.), switchgrass (Panicum virgatum L.), caucasian bluestem (Bothriochloa caucasia L.), reed canarygrass (Phalaris arundinacea L.), ladino clover (Trifolium repens L.), birdsfoot trefoil (Lotus corniculatus L.), crownvetch (Coronilla varia L.), alfalfa (Medicago sativa L.), common sericea lespedeza and AULotan sericea lespedeza (Lespedeza cuneata L.), tall fescue-ladino clover, tall fescue-alfalfa, orchardgrass-birdsfoot trefoil, switchgrass-AULotan, and an herbaceous species mix intended for planting on reforested sites consisting of foxtail millet [Setaria italica (L.) Beauv.], perennial ryegrass (Lolium perenne L.), redtop (Agrostis alba L.), kobe lespedeza (Kummerowia striata L.), appalow lespedeza (Lespedeza cuneata L.), and birdsfoot trefoil were established between spring 1990 and 1991. Vegetative biomass and/or persistence were assessed in 1996, 1997, 1998, 2000, 2001, and 2002. The high rate of biosolids applied provided favorable soil chemical properties but could not overcome physical property limitations due to shallow undeveloped soil perched atop a compacted soil layer at 25 cm depth. The plant species whose persistence and biomass production were the greatest after a decade or more of establishment (i.e., switchgrass, sericea lespedeza, reed canarygrass, tall fescue, and crownvetch) shared the physiological and reproductive characteristics of low fertility requirements, drought and moisture tolerance, and propagation by rhizome and/or stolons. Of these five species, two (tall fescue and sericea lespedeza) are or have been seeded commonly on Appalachian coal surface mines, and often dominate abandoned pasture sites. Despite the high rates of heavy metal-bearing biosolids applied to the soil, plant uptake of Cd, Cu, Ni, and Zn were well within critical concentrations more than a decade after establishment of the vegetation.     

Biosolids effects on phosphorus retention and release in some sandy Florida soils

The soil solid phase components most responsible for P sorption in Florida soils are Fe and Al oxides. Thus, we hypothesized that land application of biosolids would significantly increase a soil's P retention by increasing its content of P-sorbing solids, especially when biosolids with high Fe and Al concentrations are applied to soils that sorb P poorly. Biosolids effects were quantified by a series of single-point isotherms on soils from two field studies sampled for up to 4 yr after initial biosolids application. Biosolids additions had little effect on P retention in a soil with abundant oxalate-extractable Fe and Al and a correspondingly large native P-sorbing capacity. However, biosolids significantly increased P retention in a soil with low oxalate-extractable Fe and Al content and low native P-sorbing capacity. Biosolids effects on P retention lasted 1 to 3 yr after application, depending on biosolids source and rate of application, and generally mimicked persistence of increased extractable Fe and Al concentrations in the poorly P-sorbing soil. Disappearance of added Fe and Al (and, hence, P retention capacity) from the surface horizons over time was relatively rapid, perhaps due to abundant organic acid production associated with biosolids degradation. Phosphorus in biosolids containing (or tailored to contain) abundant Fe and/or Al can be expected to behave as a slowly available P source, and to be less subject to leaching losses than completely soluble P sources.     

Adsorption of cadmium on biosolids-amended soils

Debate exists over the biosolid phase (organic or inorganic) responsible for the reduction in phytoavailable Cd in soils amended with biosolids as compared with soils amended with inorganic salts. To test the importance of these two phases, adsorption isotherms were developed for soil samples (nine biosolids-amended soils and their five companion controls) and two biosolids samples from five experimental sites with documented histories of biosolids application. Subsamples were treated with 0.7 M NaClO to remove organic carbon. Cadmium nitrate was added to both moist soil samples and their soil inorganic fractions (SIF) in a 0.01 M Ca(NO3)2 solution at three pH levels (6.5, 5.5, and 4.5), and equilibrated at 22 +/- 1 degrees C for at least 48 h. Isotherms of Cd adsorption for biosolids-amended soil were intermediate to the control soil and biosolids. Decreasing pH did not remove the difference between these isotherms, although adsorption of Cd decreased with decreasing pH level. Organic matter removal reduced Cd adsorption on all soils but had little influence on the observed difference between biosolids-amended and control soils. Thus, increased adsorption associated with biosolids application was not limited to the organic matter addition from biosolids; rather, the biosolids application also altered the adsorptive properties of the SIF. The greater affinity of the inorganic fraction of biosolids-amended soils to adsorb Cd suggests that the increased retention of Cd on biosolids-amended soils is independent of the added organic matter and of a persistent nature.     

Assessment of the use of industrial by-products to remediate a copper- and arsenic-contaminated soil

Two water treatment sludges (WTS-A, WTS-B), two red muds (RM), and red gypsum (RG), all rich in iron oxy-hydroxides, were added to a soil highly polluted with As and Cu at 2% (w/w) to reduce metal bioavailability. Because the amendments increased soil pH to approximately 6, a lime treatment to the same pH and an unamended treatment were included for comparison. All the amendments had significant positive effects on the soil microbial biomass and growth of ryegrass (Lolium multiflorum Lam. cv. Avance), but only WTS-A improved lettuce (Lactuca sativa L. cv. Tom Thumb) growth. The mineralization of added ammonium nitrogen was not significantly affected by the treatments, while a physiologically based extraction test (PBET) showed that bioaccessibility of As was low (< 5%) and decreased only in the WTS-A treatment. Concentrations of As in soil pore water and extractable As only decreased in the WTS and RG treatments. In contrast, Cu concentrations in soil pore water and extractable Cu decreased in all treatments, by more than 84% in the WTS, RM, and RG treatments. Non-isotopically exchangeable As and Cu were present in colloids in the soil pore water. Untreated soil had < 4% isotopically exchangeable As and this decreased by approximately 50%, with WTS, RM, and RG. The labile Cu pool represented a large proportion (34%) of the total Cu pool, and the isotopically exchangeable and soluble Cu were strongly correlated with soil pH. Acidification of the treated soils showed that the labile As and Cu both increased in the treated soils compared with untreated soils. The significance of the treatment effects on soil fertility and potential off-site transport of As and Cu to ground water are discussed.     

CONTROLLING PHOSPHORUS IN RUNOFF FROM LONG TERM DAIRY WASTE APPLICATION FIELDS1

ABSTRACT: Phosphorus (P) in runoff from long term animal waste application fields can contribute to accelerated eutrophication of surface waters. Manure when applied at nitrogen (N) agronomic rates generally increases soil P concentrations, which can increase runoff of soluble P. Along the North Bosque River in central Texas, dairy waste application fields are identified as the most controllable nonpoint source of soluble P in a total maximum daily load. To evaluate P reduction practices for fields high in soil extractable P, edge‐of‐field runoff was measured from paired plots of Coastal bermudagrass (Cynodon dactylon) and sorghum (Sorghum bicolor)/ winter wheat (Triticum spp.). Plots (about 0.4 ha) received manure at P agronomic rates following Texas permit guidelines and commercial N during the pretreatment period. During the post‐treatment period, control plots continued to receive manure at P agronomic rates and commercial N. Treatment plots received only commercial N during the post‐treatment period. Use of only commercial N on soils with high extractable P levels significantly decreased P loadings in edge‐of‐field runoff by at least 40 percent, but runoff concentrations sometimes increased. No notable changes in extractable soil P concentrations were observed after five years of monitoring due to drought conditions limiting forage uptake and removal.     

Effect of amendment of bauxite processing sand with organic materials on its chemical,physical and microbial properties

The effects of addition of a range of organic amendments (biosolids, spent mushroom compost, green waste compost and green waste-derived biochar), at two rates, on some key chemical, physical and microbial properties of bauxite-processing residue sand were studied in a laboratory incubation study. Levels of exchangeable cations were not greatly affected by additions of amendments but extractable P was increased significantly by mushroom and green waste composts and massively (i.e. from 11.8 to 966 mg P kg^?1) by biosolids applications. Levels of extractable NO₃^?–N were also greatly elevated by biosolids additions and there was a concomitant decrease in pH. Addition of all amendments decreased bulk density and increased mesoporosity, available water holding capacity and water retention at field capacity (?10 kPa), with the higher rate having a greater effect. Addition of biosolids, mushroom compost and green waste compost all increased soluble organic C, microbial biomass C, basal respiration and the activities of β-glucosidase, L-asparaginase and alkali phosphatase enzymes. The germination index of watercress grown in the materials was greatly reduced by biosolids application and this was attributed to the combined effects of a high EC and high concentrations of extractable P and NO₃^?. It was concluded that the increases in water storage and retention and microbial activity induced by additions of the composts is likely to improve the properties of bauxite-processing residue sand as a growth medium but that allowing time for soluble salts, originating from the organic amendments, to leach out may be an important consideration before sowing seeds.     

Fate of biosolids trace metals in a dryland wheat agroecosystem

Biosolids land application for beneficial reuse applies varying amounts of trace metals to soils. Measuring plant-available or total soil metals is typically performed to ensure environmental protection, but these techniques do not quantify which soil phases play important roles in terms of metal release or attenuation. This study assessed the distribution of Cd, Cr, Cu, Mo, Ni, Pb, and Zn associated with soluble/exchangeable, specifically adsorbed/carbonate-bound, amorphous Mn hydroxyoxide-bound, amorphous Fe hydroxyoxide-bound, organically complexed, and residual inorganic phases. Biosolids were applied every 2 yr from 1982 to 2002 (except in 1998) at rates of 0, 6.7, 13.4, 26.8, and 40.3 dry Mg biosolids ha(-)(1) to 3.6- by 17.1-m plots. In 2003, 0- to 20-cm and 20- to 60-cm soil depths were collected and subjected to 4 mol L(-1) HNO(3) digestion and sequential extraction. Trace metals were concentrated in the 0- to 20-cm depth, with no significant observable downward movement using 4 mol L(-1) HNO(3) or sequential extraction. The sequential extraction showed nearly all measurable Cd present in relatively mobile forms and Cr, Cu, Mo, Ni, Pb, and Zn present in more resistant phases. Biosolids application did not affect Cd or Cr fractionation but did increase relatively immobile Cu, Mo, and Zn phases and relatively mobile Cu, Ni, and Pb pools. The mobile phases have not contributed to significant downward metal movement. Long-term, repeated biosolids applications at rates considered several times greater than agronomic levels should not significantly contribute to downward metal transport and ground water contamination for soils under similar climatic conditions, agronomic practices, and histories.     

Relationships between biosolids treatment process and soil phosphorus availability

Laws mandating phosphorus (P)-based nutrient management plans have been passed in several U.S. Mid-Atlantic states. Biosolids (sewage sludge) are frequently applied to agricultural land and in this study we evaluated how biosolids treatment processes and biosolids P tests were related to P behavior in biosolids-amended soils. Eight biosolids generated by different treatment processes, with respect to digestion and iron (Fe), aluminum (Al), and lime addition, and a poultry litter (PL), were incubated with an Elkton silt loam (fine-silty, mixed, active, mesic Typic Endoaquult) and a Suffolk sandy loam (fine-loamy, siliceous, semiactive, thermic Typic Hapludult) for 51 d. The amended soils were analyzed at 1 and 51 d for water-soluble phosphorus (WSP), iron-oxide strip--extractable phosphorus (FeO-P), Mehlich-1 P and pH. The biosolids and PL were analyzed for P, Fe, and Al by USEPA 3050 acid-peroxide digestion and acid ammonium oxalate, Mehlich-1, and Mehlich-3 extractions. Biosolids and PL amendments increased extractable P in the Suffolk sandy loam to a greater extent than in the Elkton silt loam throughout the 51 d of the incubation. The trend of extractable WSP, FeO-P, and Mehlich-1 P generally followed the pattern: [soils amended with biosolids produced without the use of Fe or Al] > [PL and biosolids produced using Fe or Al and lime] > [biosolids produced using only Fe and Al salts]. Mehlich-3 P and the molar ratio of P to [Al + Fe] by either the USEPA 3050 digestion or oxalate extraction of the biosolids were good predictors of changes in soil-extractable P following biosolids but not PL amendment. Therefore, the testing of biosolids for P availability, rather than total P, is a more appropriate tool for predicting extractable P from the biosolids-amended soils used in this study.     

Sorption and desorption of cadmium by different fractions of biosolids-amended soils

To evaluate the importance of both the inorganic and organic fractions in biosolids on Cd chemistry, a series of Cd sorption and desorption batch experiments (at pH 5.5) were conducted on different fractions of soils from a long-term field experimental site. The slope of the Cd sorption isotherm increased with rate of biosolids and was different for the different biosolids. Removal of organic carbon (OC) reduced the slope of the Cd sorption isotherm but did not account for the observed differences between biosolids-amended soils and a control soil, indicating that the increased adsorption associated with biosolids application was not limited to the increased OC from the addition of biosolids. Removal of both OC and Fe/Mn further reduced the slopes of Cd sorption isotherms and the sorption isotherm of the biosolids-amended soil was the same as that of the control, indicating both OC and Fe/Mn fractions added by the biosolids were important to the increased sorption observed for the biosolids-amended soil samples. Desorption experiments failed to remove from 60 to 90% of the sorbed Cd. This "apparent hysteresis" was higher for biosolids-amended soil than the control soil. Removal of both OC and Fe/Mn fractions was more effective in removing the observed differences between the biosolids-amended soil and the control than either alone. Results show that Cd added to biosolids-amended soil behaves differently than Cd added to soils without biosolids and support the hypothesis that the addition of Fe and Mn in the biosolids increased the retention of Cd in biosolids-amended soils.     

Recovery and distribution of biosolids-derived trace metals in a clay loam soil

The long-term mobility of trace metals has been cited as a potential hazard by critics of EPA 503 rule governing the land application of biosolids. The objectives of this study were to assess the accumulation of Cu, Ni, Cd, and Zn within the soil profile; the distribution of exchangeable, specifically adsorbed, organic, and oxide fractions of each metal; and mass balance of Cu, Ni, and Zn 17 yr after a single biosolids application. Biosolids were applied to 1.5- x 2.3-m confined plots of a Davidson clay loam (fine, kaolinitic, thermic Rhodic Kandiudult) in 1984 at 0, 42, 84, 126, 168, and 210 Mg ha(-1). The highest biosolids application supplied 4.5, 750, 43, and 600 kg ha(-1) of Cd, Cu, Ni, and Zn, respectively. Soils were sampled to a depth of 0.9 m and sectioned into 5-cm increments after separating the Ap horizon. Total (EPA-3050B), bioavailable (Mehlich-I), sequential extraction, and dispersible clay analyses were performed on samples from the control, 126 Mg ha(-1), and 210 Mg ha(-1) treatments. Trace metals are still concentrated in the top 0.2 m with slight enrichment down to 0.3 m. More than 85% of applied Cu, Ni, and Zn are still found in the topsoil where biosolids was incorporated and 95% or more of the applied metals were accounted for with mass balance calculations. Mehlich-I results showed a slight increase in metal concentration down to 0.35 m. Biosolids application increased the concentrations of trace metals in all the extracted fractions. The major portions of Cu, Zn, and Ni are associated with the metal-oxides fraction. Dispersible clay content and water-soluble metal contents were low and except for water-soluble Zn they were not affected by biosolids application. Results from this study showed that 17 yr after biosolids application there was negligible movement of trace metals through the soil profile and consequently there is little risk of contamination of ground water at this site.     

Compost, manure, and gypsum application to timothy/red clover forage

Some of the most fertile agricultural land in Atlantic Canada includes dykelands, which were developed from rich salt marshes along the Bay of Fundy through the construction of dykes. A 2-yr field experiment was conducted on dykeland soil to evaluate the effect of fertility treatments: source-separated municipal solid waste (SS-MSW) compost, solid manure, commercial fertilizer, and gypsum on (1) timothy/red clover forage productivity, (2) N, S, and other nutrients uptake, and (3) residual NO(3)-N and NH(4)-N in the soil profile. All fertility treatments increased dry matter yields from the two cuts each year relative to the control. Residual soil NO(3)-N and NH(4)-N concentrations in the fall of the second year decreased with depth, and beyond 20-cm depth were lower than 1 mg kg(-1). Gypsum application equivalent to 40 kg S ha(-1) increased dry matter yields and N uptake by forage, and increased soil Mehlich 3-extractable S, tissue S, and uptake of S, Ca, P, Cu, Fe, and Mn relative to the control. High rates of compost can provide sufficient N, S, and perhaps other nutrients to a perennial forage system under the cool wet climate of Atlantic Canada with no heavy metal enrichment of forage. However, the chemical N provided greater total N uptake than organic sources, except the high rate of compost, suggesting that the N availability from organic sources was not well synchronized with forage N demand. Municipal solid waste compost may also increase soil and forage tissue Na, which might be of concern.