Gerald M. Ward

Abstract: 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 Following legal challenge, most Mo numerical standards were withdrawn, pending additional field-generated data using modern biosolids (Mo concentrations 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.

Abstract: It is widely accepted that ratios of dietary copper (Cu) to molybdenum (Mo) lower than 10:1 may produce molybdenosis in cattle, especially if sulfur concentrations are more than 3,000 ppm. Some authorities suggest that dietary Mo concentrations greater than 10 ppm are hazardous to cattle regardless of Cu concentration, but anecdotal reports suggest that this may not be the case. The original purpose of the experiment described in this report was to investigate whether supranutritional supplemental Cu could protect cattle against relatively high dietary Mo. Pregnant cows were grazed on 1 of 3 pastures: 1 with only background Mo, 1 with an average of 13 ppm Mo, and 1 that averaged 230 ppm Mo. Half the cows on the Mo pastures were supplemented with 17 ppm dietary Cu, the other half with the dietary supplement plus Cu boluses. Molybdenum effects were anticipated in the groups supplemented with 17 ppm Cu; however, despite increased tissue concentrations of Mo, only the 230 ppm Mo/17 ppm Cu group exhibited any effects. Moderate Cu supplementation permitted cows to graze a site heavily contaminated with Mo with no adverse effects on general health or reproduction.

Abstract: Tall wheatgrass (Thinopyrum ponticum, cv. ‘Jose’) (TWG) has been identified as a salt-tolerant forage that has acceptable nutritional value and shows considerable promise for reducing saline drainage volumes in California's San Joaquin Valley (SJV). The SJV drainage water also contains high concentrations of boron (B), selenium (Se) and molybdenum (Mo), which may affect the production potential and mineral nutritional value of the forage. A greenhouse study was conducted with soil-filled pots using irrigation waters that varied in B (0.7–20 mg L−1) and sodium-sulfate dominated salinity (0.5–20 dS m−1), a quality characteristic of the SJV, with a constant background of 0.5 mg L−1 Se and Mo. Our experiment confirms that TWG is very tolerant to salinity. For example forage production in treatments with irrigation water with an ECw of 10 dS m−1 (ECe of 16.8 dS m−1) was 74% of those irrigated with non-saline water. We found that the stable carbon isotope fractionation in shoot tissue was a good cumulative stress indicator of the crop as the discrimination value (Δ) decreased with increased salinity and reduced shoot biomass. Moreover, this forage crop is extremely tolerant to B, tolerating up to 20 mg L−1 in the irrigation water without a significant reduction in cumulative biomass. Tissue B concentrations increased with increased B to values above 2000 mg kg−1 dry matter (DM). However as salinity increased within a particular B treatment, tissue B decreased. Forage quality, from a ruminant mineral nutrition perspective, raised concerns. Forage samples contained high levels of B, Se, Mo and sulfur near or above the recommended maximum tolerable level (MTL). Although ruminant grazing of pastures containing forage of this quality is not recommended, it has considerable potential as a forage supplement if rations can be controlled. Livestock consuming forage of this quality should be monitored for signs of B, Se and sulfur toxicity and molybdenum–sulfur induced copper deficiency.

Abstract: High concentrations (21–44 mg kg-1 dry matter) of Mo have been identified in forage in several reclaimed mining areas in British Columbia. Since Mo concentrations greater than 5 mg kg-1 in forage dry matter may result in molybdenosis because of a secondary Cu deficiency in ruminants, a study was undertaken to determine if cattle can safely graze the reclaimed land. For 12-wk grazing periods in 1994, 1995 and 1996, 32 cow/calf pairs grazed high-Mo forage at a reclaimed mine tailings site located at the Highland Valley Copper mine near Logan lake, BC. Half of the animals in the trial received a Cu supplement (All-Trace copper bolus) and the other half served as a control group. There were no significant differences (P < 0.05) in weight gain, liver Mo, serum Cu and Mo, and milk Cu and Mo between the two treatment groups of cows. Liver Cu was higher for the Cu bolus group at certain time periods in 1994 and 1995, indicating that the bolus was effective at supplying Cu. At all times, the liver Cu levels for th...

Abstract: In the present study, 12 heavy metals (Cr, Mn, Ni, Cd, Co, Cu, Pb, Zn, Fe, Se, As, and Mo) were assessed in a potential vegetable Luffa cylindrica. The vegetable was collected randomly from two different sites located at Jhang, Punjab Pakistan. The analyses of variance of data collected from soil showed non-significant effect on Se, Zn, As, Cr, Ni, Mo and Pb while significant effect on Fe, Co, Mn, Cu and Cd metals. Concentrations of all 12 heavy metals in the soil samples were low at sampling site-I as compared to those at site-II except Ni. These concentrations were found below the safe limits except that of Cd. At site-I, the concentrations recorded for different heavy metals were: As > Fe > Pb > Mn > Cd > Co > Cu > Mo > Zn > Ni > Se > Cr while at site-II were: As > Fe > Mn > Pb > Co > Cd > Cu > Mo > Zn > Ni > Se > Cr. Enrichment coefficient of Cr was higher which showed that root of luffa plant accumulated more Cr concentration from the contaminated soil. The order of enrichment co-efficient was recorded at site-I as: Cr > Zn > Mn > Cu > Fe > Ni > Mo > Pb > As > Se > Co > Cd, and at site-II Cr > Zn > Mn > Ni > Cu > Fe > Mo > Pb > Se > As > Co > Cd. The transfer co-efficient of Mn was higher which indicates that more contents of Mn were transferred from roots to upper edible part. The order of transfer coefficient at site-I was: Ni > Se > Mo > Cr > Zn > Fe > Mn > Cd > Pb > As > Cu > Co and at site-II was Mn > Zn > As > Fe > Pb > Se > Cd > Co > Mo > Cu > Ni > Cr. Correlation analysis showed that Mn, Se, Co, Cd, Ni, Mo and Pb had positive non-significant correlation, whereas a negative and non-significant correlation for Zn, As, Fe and Cr. The order of pollution load index at site-I was Cd > Mo > Se > Pb > Cu > Co > As > Fe > Mn > Ni > Zn > Cr and at site-II: Cd > Mo > Se > Pb > Cu > Co > As > Fe > Mn > Ni > Zn > Cr. Overall, at both sites, lowest concentration of Cr and highest of As were observed which need substantial awareness. Health risk index depends on soil characteristics, chemical composition, rate of consumption and type of a vegetable. In the present study, the order of health risk index due to these heavy metals at site-I was as As > Mo > Mn > Pb > Ni > Cd > Zn > Se > Fe > Co > Cr > Cu and at site-II as As > Mn > Mo > Pb > Cd > Zn > Ni > Se > Fe > Co > Cr > Cu.