Field Studies Measuring the Aerosolization of Endotoxin During the Land Application of Class B Biosolids.

Endotoxins are a component of Gram-negative bacteria cell walls and are known to be present in biosolids. Endotoxins have been shown to be potent stimulators of the innate immune response causing airway irritation and shortness of breath. Class B biosolids are routinely applied to agricultural lands to enhance soil properties and can be used as an alternative to chemical fertilizers. This study investigated the aerosolized endotoxin dispersed during the land application of Class B biosolids on agricultural land and a concrete surface at two sites in Colorado, USA. Aerosolized endotoxin was captured using HiVol samplers fitted with glass fiber filters, polycarbonate filter cassettes (both open and closed) and BioSampler impinger air samplers. Endotoxins were also measured in the biosolids to allow for correlating bulk biosolids concentrations with aerosol emission rates. Endotoxin concentrations in biosolids, impinger solutions and filter extracts were determined using the kinetic Limulus amebocyte lysate assay. Aerosolized endotoxin concentration was detected from all sites with levels ranging from 0.5 to 642 EU/m3. The four types of sampling apparatus were compared, and the HiVol and open-faced cassette samplers produced higher time-weighted average (TWA) measurements (EU/m3) than the impinger and closed cassette samplers. Ambient wind speed was found to be the variable best describing the observed results with optimal wind speed for highest deposition estimated at 5 m s-1. It is argued that HiVol air samplers are a particularly reliable approach and subsequent analyses relating TWA measurements to wind speed and biosolids characteristics were based on the measurements collected with those samplers.

Copper and zinc speciation in a biosolids-amended, semiarid grassland soil.

Predicting trace-metal solid-phase speciation changes associated with long-term biosolids land application is important for understanding and improving environmental quality. Biosolids were surface-applied (no incorporation; 0, 2.5, 5, 10, 21, and 30 Mg ha) to a semiarid grassland in 1991 (single application) and 2002 (repeated application). In July 2003, soils were obtained from the 0- to 8-, 8- to15-, and 15- to 30-cm depths in all plots. Using soil pH, soluble anion and cation concentrations from 0.01 mol L CaCl extractions, dissolved organic C (DOC) content, and an estimate of solid phase humic and fulvic acids present, Cu and Zn associated with minerals, hydrous ferric oxides (HFO), organically complexed, electrostatically bound to organic matter (OM), or DOC phases was modeled using Visual Minteq. Scanning electron microscopy and energy-dispersive X-ray analysis (SEM-EDXRA) was also used to identify solid-phase metal associations present in single and repeated biosolids-amended soils. Based on soil solution chemistry in all depths, as modeled using Visual Minteq, >90% of the Cu and >95% of the Zn from the single or repeated biosolids-applied soils were sorbed electrostatically or as mono- or bidentate solid-phase OM complexes. Up to 10 and 5% of the Cu and Zn, respectively, was associated with HFO, with negligible amounts associated with DOC. The SEM-EDXRA of clay-sized separates from all soil depths led to direct observation of Fe-Cu and Fe-Zn associations. Results implied that after surface-applying biosolids either once or twice with up to 30 Mg ha, some shifts occurred in phases controlling Cu and Zn solubility, but solution concentrations remained below drinking water standards.

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, NO(3)-N, NH(4)-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 NO(3)-N and NH(4)-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.

Plant and soil responses to biosolids application following forest fire.

Soil stability and revegetation is a great concern following forest wildfires. Biosolids application might enhance revegetation efforts and enhance soil stability. In May 1997, we applied Metro Wastewater Reclamation District (Denver, CO, USA) composted biosolids at rates of 0, 5, 10, 20, 40, and 80 Mg ha(-1) to a severely burned, previously forested site near Buffalo Creek, CO to improve soil C and N levels and help establish eight native, seeded grasses. The soils on the site belong to the Sphinx series (sandy-skeletal, mixed, frigid, shallow Typic Ustorthents). Vegetation and soils data were collected for four years following treatment. During the four years following treatment, total plant biomass ranged from approximately 50 to 230 g m(-2) and generally increased with increasing biosolids application. The percentage of bare ground ranged from 4 to 58% and generally decreased with increasing biosolids rate. Higher rates of biosolids application were associated with increased concentrations of N, P, and Zn in tissue of the dominant plant species, streambank wheatgrass [Elymus lanceolatus (Scribn. & J.G. Sm) Gould subsp. lanceolatus], relative to the unamended, unfertilized control. At two months following biosolids application (1997), total soil C and N at soil depths of 0 to 7.5, 7.5 to 15, and 15 to 30 cm showed significant (P < 0.05) linear increases (r2 > 0.88) as biosolids rate increased. The surface soil layer also showed this effect one year after application (1998). For Years 2 through 4 (1999-2001) following treatment, soil C and N levels declined but did not show consistent trends. The increase in productivity and cover resulting from the use of biosolids can aid in the rehabilitation of wildfire sites and reduce soil erosion in ecosystems similar to the Buffalo Creek area.

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.