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Journal of Environmental Quality Abstract - REVIEWS AND ANALYSES

A Modified Risk Assessment to Establish Molybdenum Standards for Land Application of Biosolids


This article in JEQ

  1. Vol. 30 No. 5, p. 1490-1507
    Received: June 15, 2000

    * Corresponding author(s): gao@ufl.edu
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  1. George A. O'Connor *a,
  2. Robert B. Brobstc,
  3. Rufus L. Chaneyc,
  4. Ron L. Kincaidd,
  5. Lee R. McDowellb,
  6. Gary M. Pierzynskie,
  7. Alan Rubinc and
  8. Gary G. Van Riperf
  1. a Soil and Water Science Dep., Univ. of Florida, P.O. Box 110510, Gainesville, FL 32611
    c USDA/ARS, Beltsville, MD 20705
    d Dep. of Animal Sci., Washington State Univ., Pullman, WA 99164
    b Dep. of Animal Science, Univ. of Florida, P.O. Box 110510, Gainesville, FL 32611
    e Dep. of Agronomy, Kansas State Univ., Manhattan, KS 66506
    f Montgomery Watson, Lakewood, CO 80228


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 Following legal challenge, most Mo numerical standards were withdrawn, pending additional field-generated data using modern biosolids (Mo concentrations 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

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Copyright © 2001. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyPublished in J. Environ. Qual.30:1490–1507.