Monitoramento ambiental de espécies de Hg na laguna Mundaú (Alagoas, Brasil) e avaliação do potencial de nanopartículas de selênio (SeNPs) como inibidoras de urease para produção de fertilizantes de eficiência aumentada

Abstract

The disordered growth of urbanisation is a megatrend that is reflected in aspects such as the search for greater food production, which is still not enough to satisfactorily serve the world's population, ontributing to social inequality, food insecurity and environmental pollution processes such as nitrogen (N) losses through volatilisation, and the increase in anthropogenic activities that have caused deterioration processes in the different environmental compartments, including contamination by potentially toxic elements such as mercury (Hg). Studies in the environmental field are therefore urgently needed. The present work developed a laboratory scale study to evaluate the potential of SeNPs and SeCuNPs as inhibitors of Jack bean (Canavalia ensiformis) urease, as well as monitoring total Hg, inorganic Hg (HgI) and by difference estimating organic Hg (HgO) in water samples from the Mundaú Manguaba Estuarine Lagoon Complex (CELMM). In order to assess the inhibitory potential of the NPs, a screening was carried out with different concentrations (0.01 to 5000 μg L-1) of SeNPs and SeCuNPs against urease to determine the IC50, where a value of 5880 ± 570 and 0.83 ± 0.05 μg L-1 was obtained, respectively. The classic inhibitors NBPT (159 ± 2 μg L-1) and Hydroxyurea (298 ± 4 μg L-1) were used for comparison. To evaluate the effect of organic matter on urease, humic substances (HS) were used at 100 mg L-1and the new IC50 values for SeNPs, SeCuNPs, NBP and HU were 4870 ± 130, 890 ± 10, 1670 ± 80 and 5610 ± 90 mg L-1 , respectively. The kinetic studies show that both NPs have a mixed type of inhibition, with SeNPs having a greater affinity for the free enzyme (KI = 0.23 ± 0.02 and KI‘ = 0.57 ± 0.07 μg L -1) and SeCuNPs having a greater affinity for the enzyme-substrate complex (KI = 2.90 ± 0.04 and KI’ = 0.52 ± 0.03 μg L-1). Finally, four soil samples with different physico-chemical characteristics were used to evaluate the effect of NPs and NBPT on the inhibition of ureases present in these soils and, in general, the NPs showed inhibitory percentages comparable to the NBPT values for all the soils. With regard to the results of the water analyses in the CELMM, the average concentration (μg L-1 ) of total Hg, HgI and HgO, respectively, were: sample 1 (1.97, 0.37 and 1. 60.00), sample 2 (2.31, 0.42 and 1.90), sample 3 (0.63, 0.07 and 0.58), sample 4 (0.29; 0.014 e 0.025), sample 5 (0.079; 0.017 e 0.026), sample 6 (0.24; ND, 0.24) and sample 7 (0.15; ND e 0.15). Most of these results are higher than the 0.02 μg L-1allowed by current Brazilian legislation (CONAMA 357/05) and comparing these results with the work of Silva et al. (2021), where the authors determined the concentration of total Hg in water samples from the CELMM analyzed in 2017, in the last four years there has been an increase of up to 150 times in the concentration of total Hg. Even more alarmingly, HgO was the majority fraction determined, and this is the most toxic form. Given the results obtained for the study of urease inhibition by NPs, it can be inferred that SeNPs proved to be a promising nanomaterial for the development of fertilisers with increased efficiency. Based on the results obtained in the CELMM monitoring study, it can be said that emergency public policies are needed so that, together with the scientific and local community, alternatives can be developed to remedy this problem.