Reducing Potential Leaching of Phosphorus, Heavy Metals, and Fecal Coliform From Animal Wastes Using Bauxite Residues

Metagenomic insights into the microbial community structure and resistomes of a tropical agricultural soil persistently inundated with pesticide and animal manure use

Persistent use of pesticides and animal manure in agricultural soils inadvertently introduced heavy metals and antibiotic/antibiotic resistance genes (ARGs) into the soil with deleterious consequences. The microbiome and heavy metal and antibiotic resistome of a pesticide and animal manure inundated agricultural soil (SL6) obtained from a vegetable farm at Otte, Eiyenkorin, Kwara State, Nigeria, was deciphered via shotgun metagenomics and functional annotation of putative ORFs (open reading frames). Structural metagenomics of SL6 microbiome revealed 29 phyla, 49 classes, 94 orders, 183 families, 366 genera, 424 species, and 260 strains with the preponderance of the phyla Proteobacteria (40%) and Actinobacteria (36%), classes Actinobacteria (36%), Alphaproteobacteria (18%), and Gammaproteobacteria (17%), and genera Kocuria (16%), Sphingobacterium (11%), and Brevundimonas (10%), respectively. Heavy metal resistance genes annotation conducted using Biocide and Metal Resistance Gene Database (BacMet) revealed the detection of genes responsible for the uptake, transport, detoxification, efflux, and regulation of copper, cadmium, zinc, nickel, chromium, cobalt, selenium, tungsten, mercury, and several others. ARG annotation using the Antibiotic Resistance Gene-annotation (ARG-ANNOT) revealed ARGs for 11 antibiotic classes with the preponderance of β-lactamases, mobilized colistin resistance determinant (mcr-1), macrolide-lincosamide-streptogramin (MLS), glycopeptide, and aminoglycoside resistance genes, among others. The persistent use of pesticide and animal manure is strongly believed to play a major role in the proliferation of heavy metal and antibiotic resistance genes in the soil. This study revealed that agricultural soils inundated with pesticide and animal manure use are potential hotspots for ARG spread and may accentuate the spread of multidrug resistant clinical pathogens.

Content of heavy metals in animal feeds and manures from farms of different scales in northeast China

To determine the contents of heavy metal (Cu, Zn, As, Cr, Cd and Pb) in animal feeds and manures, 104 livestock feeds and 118 animal manure samples from farms of different herd size and located in northeast China were collected and their heavy metal concentrations were determined. The content of Cu, As and Cd ranged from 2.3–1,137.1 mg/kg dm, 0.02–13.03 mg/kg dm and non-detectable (nd)−31.65 mg/kg dm in pig feeds, 2.88–98.08 mg Cu/kg dm, 0.02–6.42 mg As/kg dm and non-detectable (nd)–8.00 mg Cd/kg dm in poultry feeds, and their content in cattle feeds was similar to that in poultry feeds. The typical content in pig manures was 642.1 mg Cu/kg dm, 8.6 mg As/kg dm, and 15.1 mg Cd/kg dm, which reflected the metal contents in feeds. The typical contents in poultry manures were 65.6 mg Cu/kg dm, 3.3 mg As/kg dm and 1.6 mg Cd/kg dm while the contents in cattle manures were 31.1 mg Cu/kg dm, 2.5 mg As/kg dm and 0.5 mg Cd/kg dm. Animal manure is an important source of heavy metals to the environment in Northeast China.

Use of inorganic wastes as immobilizing agents for soluble P in green waste-based composts

PURPOSE

The study examines the effectiveness of red mud, blast furnace (BF) slag, and alum-derived water treatment sludge as immobilizing agents for excessive soluble P that had accumulated in three green waste-based composts.

METHODS

The three wastes were applied at 0%, 5%, 10%, and 20% w/w to three different composts, all containing extremely high concentrations of extractable P, and were incubated for 60 days. Water-soluble P was measured regularly throughout the incubation period, and at the end, P extractable with resin, 0.05 M NaHCO(3), and 0.005 M H(2)SO(4) were also measured.

RESULTS

In the water extracts, inorganic P made up more than 85% of the total P present. All three materials had the ability to adsorb P and thus lowered water-soluble P concentrations. Water treatment sludge was clearly the most effective material, and this was attributed to its amorphous nature (thus, large Brunauer-Emmett-Teller surface area) and its acid pH (6.8) compared with the alkaline pH (10-11) of the other two materials. Water treatment sludge was also the most effective at lowering resin- and NaHCO(3)-extractable P. When H(2)SO(4) was used as the extractant, BF slag tended to be the most effective material at lowering extractable P, followed by water treatment sludge, and red mud. That is, the P immobilized by water treatment sludge was extractable with acid but not with water, resin, or NaHCO(3).

CONCLUSIONS

Water treatment sludge has the potential to be used as an effective immobilizing agent for soluble P in composts, and it should be trialed under field conditions.