History of vinasse application in sugarcane crops: terrestrial and aquatic toxicity bioassays

Author(s)

Jorge Evangelista Correia

• Document type: Doctoral Thesis
• Press: Rio Claro. 2020-03-18.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Rio Claro
• Defense date: 2019-12-29
• Advisor: Carmem Silvia Fontanetti Christofoletti; Jarbas Honorio de Miranda

Abstract

Vinasse, one of the main residues generated in the transformation of sugarcane into ethanol, has a pollution potential, given its high byproduct volume and its physicochemical characteristics. The contamination of lakes and rivers, by infiltration of waste disposed in the soil, such as vinasse and fertilizers, for example, deserves attention. Since the prohibition on the disposal of vinasse in water in the 1980s, this residue has been used as fertilizer in sugarcane crops. Currently this practice will complete 40 years and only in 2006 legislation regulating the fertigation of vinasse was created. The toxic potential of vinasse, both in soil and water, has been proven by several studies in the last decade, but studies that relate time to toxicity are necessary. In view of this, this study aimed to understand this study aimed to understand if the years vinasse fertigation alter the toxicity in the soil, the potassium ion dynamics in the soil and the toxicity of the vinasse leachate that can reach groundwater. For this, soils of sugarcane crops fertigated with vinasse for 5, 15 and 30 years were collected to perform the terrestrial toxicity bioassay and soil physics studies. control area (SC). Physical-chemical analysis of the different soil samples were performed. The bioassays were carried out in triplicate, with exposure for 21 and 42 days. After exposure, three individuals from each terrarium were anesthetized and dissected for midgut removal for histopathological analysis and marking of HSP70. The soils presented varied concentrations of organic components and metals. After 21 days only three individuals survived to soil S30 and after 42 days high mortality there was also observed in the treatment with soil S15. Histopathological analysis showed thickening of the brush border of epithelial cells statistically significant for individuals exposed to the S5 and S15 soils for 21 days. Loss of epithelial cell adhesion was statistically significant in individuals exposed to S15 for 21 days and S5 for 42 days. Potassium ion dynamics was investigated by analyzing its transport parameters, obtained by numerical adjustment of the Breakthrough Curves (BTC) by applying the CFITIM code within the STANMOD (STudio of ANalytical MODels) software and the HYDRUS-1D model. In the segmented column assays the difference between the reference soil and the fertigated soils was in the potassium concentration in the inferior rings, being higher in the fertigated soils, indicating a higher potassium mobility in these soils. In the BTC's assays, it was observed in the simulation curves that potassium concentration reached 100% of the input values for almost all triplicates of all soils. Equilibrium was reached faster in S5 than in reference soil and even faster in S15. In contrast, the soil S30 presented the highest interaction of potassium ion with the soil, confirmed by presenting the highest values of retardation coefficient (R) and distribution coefficient being statistically significant when compared between them. After the soil physics tests, the leachate obtained in the BTC's columns was tested on 5% dilution in aquatic toxicity bioassay using Oreochromis niloticus as a bioindicator and incidence of micronucleated erythrocytes and histological changes and quantification of stress proteins in liver as biomarkers. The results showed genotoxic action of vinasse leachate after passage in soils of 5 and 15 years, demonstrated by the higher incidence of micronucleated erythrocytes, statistically significant when compared to the control. The micronuclei were possibly formed by aneugenic action, since there was no clastogenic action confirmed by the comet assay. Fish exposed to leachate from 15-year-old soil showed a statistically significant change rate for cell boundary loss and increased cytoplasmic vacuoles when compared to control. All treatments showed statistically significant increase in nuclei of hepatocytes compared to control. There was no difference in the marking of neutral polysaccharides evidenced by the PAS technique. Although not statistically significant, an activity pattern was observed for all enzymes present in this study. Enzyme activity was higher in the treatment with 15-year-old soil vinasse leachate and the lowest values in the 30-year-old soil leachate treatment. Looking at the results holistically, we can infer that over the years of vinasse application, the toxic potential in soil is inversely of groundwater toxicity, since the trend is that more and more of the vinasse components may become more retained in the soil due to the accumulation of organic matter and positively charged ions such as potassium and calcium. This behavior also raises the alert for soil salinization over time, and may in the longer term affect sugarcane production itself. (AU)

• FAPESP's process: 15/26157-9 - Relationship between the vinasse toxicity and application time in sugarcane crops: aquatic and land toxicity bioassays
• Grantee: Jorge Evangelista Correia
• Support Opportunities: Scholarships in Brazil - Doctorate