Understanding the behaviour of herbicides in the soil can contribute to adapting the correct dose for efficient weed control with less environmental impact. In this study, we sought to evaluate the factors involved in the sorption, desorption, half-life and leaching processes of sulfometuron-methyl in three soil classes: Cambissolo Háplico (CX) (Inceptisol), Latossolo Vermelho (LV) (Oxisol) and Neossolo Quartzarênico (RQ) (Entisol). The sorption and desorption tests were performed using the “batch equilibrium" method. The studies of degradation and formation of metabolites were estimated from the half-life at the end of 180 days. Leaching potential was estimated by testing PVC columns filled with soil. Analyses were performed by ultra-performance liquid chromatography coupled to a mass spectrometer for herbicide quantification. The higher sorption of sulfometuron-methyl in LV (2.81) is related to the low pH (4.7) and mineralogical composition, mainly due to the higher concentration of Fe and Al oxides in this soil, influencing the lower desorption of the herbicide in LV (0.59). This result contributed to more remarkable herbicide persistence in this soil, reducing the molecules available in the solution for degradation. These results contributed to the longer half-life (19 days) in LV compared to the other soils. Among the studied soils, RQ had the highest risk of transport of sulfometuron-methyl based on the GUS Index (2.2) due to its greater desorption (0.34). The results showed that the studied processes are dependent on the physical, chemical and mineralogical attributes of the different classes of soils.

Limited chemical control options and high onion sensitivity to post-emergence herbicides hinder efficient weed management, especially under direct-seeding systems in semi-arid regions, increasing production costs. Reduced herbicide rates and split applications may improve crop selectivity while maintaining weed control. This study aimed to evaluate the selectivity of post-emergence herbicides applied at different doses and phenological stages in onion grown under Brazilian semi -arid conditions. Four field experiments were conducted in a randomized block design with three replications, each evaluating a single herbicide (oxyfluorfen, flumioxazin, pendimethalin, or oxadiazon). Fifteen treatments were evaluated, combining herbicide doses with three application timings (1-2, 3, and 5 fully expanded leaves), plus an untreated control. Crop injury was visually assessed at 7, 14, 21, and 28 days after application (DAA). Mild phytotoxicity symptoms (< 10%) were observed mainly at early growth stages, particularly when applications were performed at the 1- or 2-leaf stage, while treatments applied at more advanced stages (3 to 5 leaves) caused little or no injury. Symptoms were transient, with recovery observed by 21 DAA. Sequential applications occasionally prolonged low -intensity injury but did not exceed acceptable levels. No significant differences in commercial yield were detected among treatments. Bulb classification was predominantly concentrated in Class 3 (50-70 mm), with values generally above 60%, indicating high commercial quality and uniformity. The results demonstrate that the evaluated herbicides were selective for onion under semi-arid conditions when applied at appropriate doses and growth stages, with early stages being more sensitive and later stages more tolerant, without compromising yield or bulb quality.

Triazine herbicides are widely used for weed control in agricultural systems, and their occurrence in water bodies has been frequently reported worldwide. This study assessed the efficiency of a hydrochar derived from the epicarp and mesocarp of passion fruit residues for the removal of three triazine herbicides (atrazine, ametryn, and metribuzin), with the aim of developing a material suitable for application in water remediation programs. The adsorption capacity of biomass and hydrochar derived from passion fruit residues was evaluated with and without activation using 0.5 mol L⁻¹ phosphoric acid. The adsorption of herbicides was not significantly affected by pH within the range of 4 to 8. The acid hydrochar, which exhibited the highest removal capacity among the evaluated adsorbents, presented adsorption capacities of 18.05, 10.83, and 5.05 µg g⁻¹ for atrazine, ametryn, and metribuzin, respectively. These values correspond to removal efficiencies of approximately 62%, 72%, and 52% at initial concentrations of 0.33, 0.25, and 0.15 mg L⁻¹. The adsorption equilibrium time varied among the herbicides, reaching 4 h for atrazine and ametryn and 5 h for metribuzin. The adsorption dynamics between the adsorbents and adsorbates were best described by the pseudo-second-order kinetic model for ametryn and metribuzin, while atrazine had a higher correlation with the Elovich equation. The Weber–Morris model did not adequately describe the adsorption process. Among the isotherms tested, the Freundlich model provided the best fit for all three herbicides. The desorption rates of the acid hydrochar were 51%, 13%, and 83% for atrazine, ametryn, and metribuzin, respectively. Therefore, hydrochar derived from passion fruit residues represents a promising alternative for the remediation of triazine herbicides.

A disposição de forma inadequada dos resíduos de construção e demolição (RCD) resulta em impactos negativos ao meio ambiente e, em decorrência, à sociedade. Nesse contexto, objetivou-se elaborar uma proposta de distribuição espacial de pontos de entrega voluntária (PEV) para recebimento de RCD no município de Mossoró-RN, com um delineamento metodológico abrangente, aplicável a outros municípios. A metodologia consistiu no mapeamento de locais com disposição inadequada de RCD na zona urbana do município, comparação e aplicação de metodologias para indicar a quantidade de PEV necessários, assim como a indicação das áreas adequadas para instalação desses dispositivos. Por meio dos resultados, verificou-se que a implementação de PEV se mostra extremamente necessária diante do número expressivo de áreas de disposição inadequada de RCD identificadas nesta pesquisa, totalizando 897 pontos. Ao término desta análise, foi indicada a instalação de 13 pontos de entrega voluntária no município de Mossoró. Palavras-chave: Obras civis. Disposição inadequada de resíduos. Sistema de informação geográfica. Gerenciamento.