Distribution and bioavailability of copper in farm effluent

Area of Science:

• Environmental Chemistry
• Soil Science
• Agricultural Science

Background:

• Dairy and piggery farming in New Zealand often utilizes copper (Cu) for animal health and growth promotion.
• This practice leads to elevated Cu concentrations in farm effluent and sludge, raising environmental concerns.
• Understanding Cu speciation and bioavailability in these waste streams is crucial for sustainable land application.

Purpose of the Study:

• To analyze copper (Cu) forms in dairy and piggery effluent and sludge from New Zealand.
• To assess the bioavailability and toxicity of sludge-borne Cu to soil microbial activity and pasture plants.
• To investigate the transformation and plant uptake of Cu from different sources in soil.

Main Methods:

• Analysis of free ionic and organically-complexed Cu in effluent and sludge samples.
• Microbial respiration experiments to determine Cu toxicity (using CuSO(4) and sludge-Cu).
• Glasshouse experiments with ryegrass to assess Cu uptake from CuSO(4), CuO, and sludge, including soil Cu fractionation.

Main Results:

• Dairy and piggery effluent/sludge showed high Cu concentrations, predominantly organically complexed.
• Sludge-Cu exhibited lower toxicity to soil microbial respiration compared to copper sulfate (CuSO(4)).
• Plant Cu uptake increased with Cu application rates from all sources; however, uptake was lower from sludge and CuO than CuSO(4).
• Sludge application led to greater accumulation of organic-bound Cu in soil.

Conclusions:

• Most copper in New Zealand dairy and piggery waste is organically bound, influencing its environmental fate.
• Copper from sludge is less bioavailable and toxic to soil microbes than inorganic copper sulfate.
• While sludge application increases soil and plant Cu, its bioavailability is lower than conventional copper fertilizers, suggesting potential for safer land application.