| Soil pollution by metals and their associated mineral flotation reagents from mining and ores processing waste discharges is of great ecological and health impacts that need to be well understood and addressed.This study aimed to analyze the soil microbial response to individual and combined effect of nickel,copper,and xanthates,sodium isoamyl xanthate(SIAX),sodium isobutyl xanthate(SIBX),sodium isopropyl xanthate(SIPX),sodium ethyl xanthate(SEX),potassium amyl xanthate(PAX),and potassium ethyl xanthate(PEX),the most efficient and commonly used sulfides mineral flotation collectors.Analysis was conducted through different complementary methods mainly the measurement of the microbial growth(cell density and viable cell counts)and enzymes activities(catalase and FDA hydrolysis),the microcalorimetric measurement of the soil microbial activities,and the molecular biology-based analysis of the structure and diversity of the soil microbes under different doses of the applied chemicals.All xanthates doses affected the soil microbial growth and enzymes activities(catalase and FDA hydrolyases activity),with a positive dose-effect relationship and an inhibition reduction trend along with the incubation time.For all analyzed parameters,PEX and SIBX were the most and least adverse,respectively.With respect to the total microbial activity,Cu,Ni,and xanthates exhibited a positive dose-effect relationship with an inhibitory concentration(IC50)of 447.5,438.69,225.76,158.3,83.95,74.08 and 39.63 for Cu,Ni,SIPX,PAX,SIAX,SEX,and PEX,respectively.Xanthates exhibited higher inhibition of the microbial activity than their corresponding mixture with metals.In most of the cases,the chemicals mixture presented a lower inhibitory ratio than the sum of the corresponding mixture components inhibitory ratios,a situation that corresponds to an antagonistic type reaction.The most individually adverse xanthate was associated with lower mixture inhibitory ratio(i.e.,PEX in case of the mixture containing Ni and SIAX in case of the mixture containing Cu).From the molecular biology-based analysis,all treated samples exhibited lower microbial richness and diversity than the control sample.The lowest values were associated with the chemical mixtures containing Cu.Different bacterial species exhibited differences in their sensitivity to different applied chemicals and doses.The six most abundant phyla were Proteobacteria(56.7%),Firmicutes(22%),Actinobacteria(10.53%),Bacteroidetes(3.26%),Acidobacteria(2.80%),and Chloroflexi(2.24%).The predominant species per sample or group of samples were Bacillusjselenatarsenatis(17%)in the control sample,unclassifiedj_g_Sphingobacterium(40.31%)in the copper-treated sample,unclassified_f_Micrococcaceae(19.97%)in the nickel-treated sample,Cupriavidus_taiwanensis(19%)in the lower xanthates-treated samples(50?.g.g-1soil),unclassified_f_Enterobacteriaceae(31%)in the higher xanthates-treated samples(100?g.g-1soil),Cupriavidus taiwanensis(45.32%)in the samples treated with lower xanthates dose in the mixture with copper,unclassified_g_Pseudomonas(51.06)in the samples amended with higher xanthates dose in the mixture with copper,Bacillus_korlensis(35.14%)in case of lower xanthates dose mixture with nickel,and Bacillus korlensis(25.04%)for the higher xanthates dose mixture with nickel.Potentially adapted or less affected bacterial species to different treatments with Cu,Ni,and xanthates,individually and in the mixture,were identified and should be subjected to further analysis to determine their resistance capability and for their potential biotechnological application. |
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