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ARS Home » Pacific West Area » Kimberly, Idaho » Northwest Irrigation and Soils Research » Research » Publications at this Location » Publication #224180
Title: Fate of biosolids Cu and Zn in a semi-arid grassland

Author
item Ippolito, James
item BARBARICK, K - COLORADO STATE UNIVERSITY
item BROBST, R - U.S. EPA

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2009
Publication Date: 3/30/2009
Citation: Ippolito, J.A., Barbarick, K.A., Brobst, R.B. 2009. Fate of biosolids Cu and Zn in a semi-arid grassland. Agriculture, Ecosystems and Environment. 131:325-332.

Interpretive Summary: In biosolids land application programs, measuring plant-available or total soil metals is typically to ensure environmental protection, yet these techniques do not quantify which soil phases are important for metal release or attenuation. Ippolito and Barbarick report that trace metals, in various soil phases, moved through the profile in experimental plots receiving single (1991) or repeated (2002) biosolids applications. 4 M HNO3 extractions suggested downward Cu transport, while Cr, Pb, and Zn appeared immobile. Sequential extraction suggested that repeated biosolids applications increased downward transport of amorphous Fe/Mn oxide-bound Cd, specifically adsorbed and residual organic Cu fractions, residual inorganic Mo, and soluble/exchangeable Ni. Increasing biosolids application increased specifically adsorbed, Fe/Mn oxides (i.e. crystalline) and acid replaceable (organically complexed), and residual organic Cu phases, and Fe/Mn oxides and acid replaceable (organically complexed) Zn transport. Because the soil was relatively coarse, downward colloidal-associated metal transport increased.

Technical Abstract: Biosolids land application applies varying trace metal amounts to soils. Measuring total soil metals is typically performed to ensure environmental protection, yet this technique does not quantify which soil phases play important metal release or attenuation roles. We assessed the distribution of biosolids-borne Cd, Cr, Cu, Mo, Ni, and Zn associated with soluble/exchangeable, specifically adsorbed, easily reducible Fe/Mn oxides, Fe/Mn oxides and acid replaceable (i.e. organically complexed), residual organic, and residual inorganic phases. Biosolids were surface-applied (no incorporation) to experimental plots in 1991 at rates of 0, 2.5, 5, 10, 21, and 30 Mg/ha. Plots were split in half in 2002, with one-half receiving biosolids at rates identical to 1991 rates. In 2003, 0-8, 8-15, and 15-30-cm soil depths were collected and subjected to 4 M HNO3 digestion and sequential fractionation. The 4 M HNO3 extraction showed increasing biosolids application rates increased Cr content, while repeated application increased Cr and Ni as compared to the single application in the 0-8-cm depth. The 4 M HNO3 extraction suggested downward Cu transport, while Cr and Zn were immobile. The sequential extraction procedure, more sensitive to changes in soil metal pools, suggested that repeated biosolids application increased the downward transport potential of easily reducible Fe/Mn oxide-bound Cd, Cu associated with specifically adsorbed and residual organic fractions, residual inorganic Mo, and soluble/exchangeable Ni. Within the 15-30-cm depth, increasing biosolids application, regardless of time applied, increased Cu associated with specifically adsorbed, Fe/Mn oxides (i.e. crystalline) and acid replaceable, and residual organic phases, and Zn associated with the Fe/Mn oxides and acid replaceable phase. The soil studied was fine-loamy over sandy/sandy-skeletal, thus the texture likely facilitated downward colloidal-associated Cd, Cu, Mo, and Zn transport. On coarse-textured semi-arid soils, biosolids application rates should match the plant N needs to avoid downward trace metal transport.