Biosolids affect soil barium in a dryland wheat agroecosystem

Area of Science:

• Environmental Science
• Soil Science
• Agronomy

Background:

• Barium (Ba) is a candidate pollutant for biosolids land application.
• Biosolids have been applied biennially to a dryland wheat-fallow agroecosystem since 1982.
• Soil Ba concentrations require monitoring due to potential environmental impacts.

Purpose of the Study:

• To monitor soil Ba concentrations in a long-term biosolids application experiment.
• To investigate the speciation and extractability of soil Ba over time.
• To assess the environmental risk of soil Ba accumulation from biosolids.

Main Methods:

• Analysis of total soil Ba using 4 M HNO(3).
• Measurement of extractable Ba using ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA).
• Soil characterization using scanning electron microscopy and wet chemistry sequential extraction.

Main Results:

• Total soil Ba increased with increasing biosolids application rates.
• Extractable soil Ba (AB-DTPA) showed significant declines over time, particularly in the upper soil layers.
• Scanning electron microscopy and sequential extraction identified insoluble Ba-S and BaCO(3) precipitates.

Conclusions:

• Biosolids application increases total soil Ba, but it forms insoluble precipitates.
• The mineral forms of Ba in the soil are not readily extractable with AB-DTPA.
• Insoluble soil Ba precipitates are unlikely to pose an environmental concern in similar agroecosystems.