Coral reefs are amongst the most biodiverse ecosystems on earth, but are significantly impacted by agricultural runoff. Despite herbicides being commonly detected in coastal waters, the possibility of herbicide accumulation in coral reef species has largely been overlooked. We investigate the accumulation of several herbicides in five species of coral reef invertebrates collected from ten sites along the Maputaland coast, South Africa. Multiple herbicide residues were detected in 95% of the samples, with total average concentrations across sites ranging between 25.2 ng g⁻¹ to 51.3 ng g⁻¹ dw. Acetochlor, alachlor and hexazinone were the predominant herbicides detected at all sites, with atrazine and simazine detected less frequently. Significant interactive effects were detected between sites nested in reef complex crossed with species, based on multiple and total herbicide concentrations. In general, multivariate herbicide concentrations varied significantly between species within and across most sites. Contrastingly, the concentrations of the different herbicides and that of total herbicide did not differ between conspecifics at most sites nested in their respective reef complexes. On average, highest total herbicide concentrations were measured in soft coral (Sarcophyton glaucum; 90.4 ± 60 ng g⁻¹ and Sinularia gravis; 42.7 ± 25 ng g⁻¹) and sponge (Theonela swinhoei; 39.0 ± 40 ng g⁻¹) species, while significantly lower concentrations were detected in hard corals (Echinopora hirsutissima; 10.5 ± 5.9 ng g⁻¹ and Acropora austera; 5.20 ± 4.5 ng g⁻¹) at most sites. Agricultural runoff entering the ocean via the uMfolozi-St Lucia Estuary and Maputo Bay are likely sources of herbicide contamination to coral reefs in the region. There is an urgent need to assess the long-term effects of herbicide exposure on coral reef communities.

Organisms and ecosystems are generally exposed to mixtures of chemicals rather than to individual chemicals, but there have been relatively few detailed analyses of the mixtures of pesticides that occur in surface waters. This study examined over 2600 water samples, analysed for between 21 and 47 pesticides, from 15 waterways that discharge to the lagoon of the Great Barrier Reef in Queensland, Australia between July 1, 2011 and June 30, 2015. Essentially all the samples (99.8%) contained detectable concentrations (>limit of detection) of pesticides and pesticide mixtures. Approximately, 10% of the samples contained no quantifiable (>limit of reporting) pesticides, 10% contained one quantifiable pesticide and 80% contained quantifiable mixtures of 2–20 pesticides. Approximately 82% of samples that contained quantifiable mixtures had more than two modes of action (MoAs), but only approximately 6% had five or more MoAs. The mode, average and median number of quantifiable pesticides in all the samples were 2, 5.1 and 4, respectively. The most commonly detected compounds both individually and in mixtures were the pesticides atrazine, diuron, imidacloprid, hexazinone, 2,4-D, and the degradation product desethylatrazine. The number of pesticides and modes of action of pesticides in mixtures differed spatially and were affected by land use. Waterways draining catchments where sugar cane was a major land use had mixtures with the most pesticides.

The impact of agricultural pesticides on sensitive aquatic ecosystems is a matter of global concern. Although South Africa is the largest user of pesticides in sub-Saharan Africa, few studies have examined the toxicological threats posed by agricultural runoff, particularly to conservation areas of international importance. This study investigated the occurrence of 11 priority listed herbicides in sediments from Lake St Lucia, located on the east coast of South Africa. While characterised by exceptionally high levels of biodiversity, Lake St Lucia is affected by agricultural runoff primarily via inflow from two major rivers; the Mkhuze and Mfolozi. Sediment samples collected from Lake St Lucia and its two major fluvial inputs reveal widespread herbicide contamination of the aquatic environment. Residues were detected in the vast majority of samples analysed, with Mkhuze (27.3 ± 17 ng g⁻¹) and Mfolozi (25.6 ± 20 ng g⁻¹) sediments characterised by similar total herbicide levels, while lower concentrations were typically detected in Lake St Lucia (12.9 ± 12 ng g⁻¹). Overall, the most prominent residues detected included acetochlor (3.77 ± 1.3 ng g⁻¹), hexazinone (2.86 ± 1.4 ng g⁻¹) and metolachlor (10.1 ± 8.7 ng g⁻¹). Ecological assessment using Risk Quotients (RQs) showed that cumulative values for triazines and anilides/aniline herbicide classes presented low to medium risk for algae and aquatic invertebrate communities. Considering the biological importance of Lake St Lucia as a nursery for aquatic organisms, it is recommended that further research on the aquatic health of the system be undertaken. Additional monitoring and investigation into mitigation strategies is suggested, particularly as agricultural activities surrounding Lake St Lucia are likely to expand in the future.

The Marine Monitoring Program (MMP) was established in 2005 to monitor the inshore health of the Great Barrier Reef (GBR) and evaluate progress towards water quality objectives in Reef Water Quality Improvement Plans. The MMP provides information on the magnitude and spatial extent of pesticide contamination, reports on temporal variability, and provides a risk assessment for the biota in the GBR lagoon. However, long-term trends in pesticide contamination of inshore marine waters over the entire monitoring period (2005–2018) have not been assessed. We used up to 14 years of monitoring data for five PSII herbicides (ametryn, atrazine, diuron, tebuthiuron, and hexazinone) to conduct temporal trend analyses at 11 inshore monitoring sites. The trend analyses suggested increasing significant trends (p < 0.05) for the five PSII herbicides concentrations at several monitoring sites. Power analysis indicated that monitoring sites with over 10 years of monitoring data had convincing results with 80% power.

Hexazinone, a globally applied broad-spectrum triazine herbicide, has not been mechanistically investigated previously under advanced oxidation processes (AOPs) and adsorption on activated carbon. In this study, its fate during UV-based oxidation with/without hydrogen peroxide (H₂O₂) and adsorption on coconut shell–based granular activated carbon (CSGAC) in water matrices was investigated. A comparison between various irradiation sources (visible, UVA, UVB, and UVC) revealed the highest degradation rate under UVC. More than 98% degradation of hexazinone was observed under 3 J cm⁻² UVC fluence in the presence of 0.5 mM H₂O₂ at pH 7. Moreover, the degradation rate enhanced significantly with an increase in the initial dosage of H₂O₂, UV fluence, and contact time in the UV/H₂O₂ process. The rate of degradation was lower using secondary effluent than that of Milli-Q water due to the presence of dissolved organics in wastewater. However, the reactions in both matrices obeyed pseudo-first-order kinetics. The effect of different scavengers, including methanol, potassium iodide (KI), and tert-butyl alcohol (TBA), showed that hydroxyl radicals (•OH) played a dominant role in hexazinone degradation in the UV/H₂O₂ process. Hexazinone was effectively adsorbed by CSGAC through π-π electron donor–acceptor interactions between hexazinone’s triazine ring and CSGAC’s surface functional groups. The isotherm and kinetic studies showed that the adsorption followed the Freundlich model and pseudo-second-order reaction, respectively, suggesting chemisorption. This study provided mechanistic insights on the removal of hexazinone at the tertiary stage of wastewater treatment or the advanced treatment of wastewater reuse.

In this study, a multi-residue method was used to analyze 13 pesticides and 1 degradation product in surface and groundwater in the region with the largest sugar cane production in the world. The potential effects of individual pesticides and their mixtures, for aquatic life and human consumption, were evaluated. For the surface water, 2-hydroxy atrazine, diuron, carbendazim, tebuthiuron, and hexazinone were the most frequently detected (100, 94, 93, 92, and 91%, respectively). Imidacloprid (2579 ng L⁻¹), carbendazim (1114 ng L⁻¹), ametryn (1101 ng L⁻¹), and tebuthiuron (1080 ng L⁻¹) were found at the highest concentrations. For groundwater, tebuthiuron was the only quantified pesticide (107 ng L⁻¹). Ametryn, atrazine, diuron, hexazinone, carbofuran, imidacloprid, malathion, carbendazim, and their mixtures presented risk for the aquatic life. No risk was observed for the pesticides analyzed in this work, alone or in their mixtures for human consumption.

Sugarcane is one of the world’s most important commodities. In order to control weeds in the plantations and increase productivity, the mixing of different herbicides during spraying operations is commonplace. This practice is unregulated, and the impact on water quality and nontarget tropical species is poorly understood. In the present work, exposure and recovery assays were used to evaluate antioxidant enzyme activity and histopathological alterations in the liver of tilapia (Oreochromis niloticus) following exposure to mixtures of the herbicides widely used in sugarcane crops: ametryn (AMT), tebuthiuron (TBUT), diuron (DIU), and hexazinone (HZN). The greatest biochemical changes were observed for the mixture (DIU+HZN)+AMT+TBUT at the highest concentration tested (1/10 96hLC50). This mixture caused a significant increase (p < 0.01) of approximately 82% in GST activity after 14 days of exposure. For three of the mixtures evaluated, GST and CAT could be considered potential biochemical biomarkers of exposure to the herbicide mixtures due to the frequency, intensity, and statistical significance of alterations in the assimilation phase. Although morphological changes were evident in the hepatic tissue, severe damage was only noted in a few samples, and there were no statistically significant differences, relative to the control. The results of hepatic lesion recovery assays suggested that the most sensitive individuals affected by the xenobiotics were unable to achieve full recovery. It is anticipated that the data obtained may assist in the selection of biomarkers for monitoring purposes, as well as in reinforcing standards of conduct in the use of agrochemical mixtures in agriculture.

The increasing use of herbicides in sugarcane production has increased environmental concern regarding the fate of these compounds, especially when they are used in mixtures. Among the various processes that determine the behavior of molecules in the environment, leaching stands out. In this context, the aim of this study was to evaluate the leaching of a mixture of hexazinone, sulfometuron-methyl, and diuron in soils with contrasting textures. A completely randomized experimental design containing three replications in a 2 × 6 factorial arrangement was used, with two soils (alfisol–Paleudult, sandy clay texture and ultisol–typic Hapludalf, sandy loam texture) and six depths (0–0.05, 0.05–0.10, 0.10–0.15, 0.15–0.20, 0.20–0.25, and 0.25–0.30 m). Three glass columns of 50 cm were used for each soil. The dose used was 391.0 + 33.35 + 1386.9 g a.i. ha⁻¹ of hexazinone, sulfometuron-methyl and diuron, respectively. After applying the mixture to the top of each column, rainfall simulation with 200 mm of 0.01 mol L⁻¹ CaCl₂ solution was applied for 48 h. The leachates were collected at 6, 12, 24, 36, and 48 h. The chromatographic determinations of the herbicides were performed by high-performance liquid chromatography (HPLC) with a UV-Vis detector. For hexazinone, the highest percentage recovery in the soil with a sandy clay texture occurred at a depth of 0.10–0.15 m, with 40 % recovered, while in the soil with a sandy loam texture, the most part was recovered at a depth of 0.25–0.30 m. Diuron demonstrated little mobility in the soil and was detected in most cases only in the surface layer (up to 0.10 m) in both soils. Sulfometuron-methyl, in soil with a sandy clay texture, was detected to a depth of 0.15–0.20 m with the highest concentration found at a depth of 0–0.05 m, while in sandy loam soil, a higher concentration was found at a depth of 0.10–0.15 m; this herbicide was detected down to 0.25–0.30 m. These results show that the soil texture directly influences the leaching of hexazinone, sulfometuron-methyl, and diuron.

Herbicides play an important role in controlling weeds in agricultural crop areas. However, the lack of knowledge of their mobility in the soil may cause environmental damage, such as the contamination of soil and water bodies. Thus, this study was conducted to identify the effect of different rainfall intensities on the leaching potential of the herbicides diuron, hexazinone, and sulfometuron-methyl in red latosol. The trials were conducted in polyvinyl chloride columns. Rainfall simulations were performed for the following intensities: 10 mm h⁻¹, 15 mm h⁻¹, 20 mm h⁻¹, and 25 mm h⁻¹ of rainfall during 4 h. The columns were sectioned into seven layers (0–0.05; 0.05–0.10; 0.10–0.15; 0.15–0.20; 0.20–0.25; 0.25–0.30; 0.30–0.35 m), and the quantification of the herbicides in the layers was performed by Ultra-High Performance Liquid Chromatography coupled to the Mass Spectrometer. The diuron showed lower leaching potential in the soil, detected almost entirely in the upper layer of the column (0.0–0.05 m) for all precipitation applied. Hexazinone showed high leaching, being detected until the last layer of the soil (0.30–0.35 m) and in the water leached in the column when applied 20 and 25 mm h⁻¹ of rainfall. Sulfometuron-methyl reached the last layer (0.30–0.35 m) when applied at an intensity of 25 mm h⁻¹. Hexazinone showed higher leaching potential and consequent environmental risk. Diuron and sulfometuron-methyl were fewer mobiles in the soil profile; however, the environmental risk should be considered because higher rainfall intensities may alter their behavior in the soil.

Sugarcane is a major crop in Brazil as well as other tropical areas. The rise of green cane systems that maintain straw on the soil surface after mechanical harvesting alongside extreme precipitation has changed the use and environmental fate of pesticides, mainly herbicides. The goal of this research was to evaluate the effects of straw amounts (0, 7, and 14 t ha⁻¹), soil water contents (10 and 18%, volumetric basis), and herbicide incubation time (0 and 3 days) on the runoff of hexazinone and diuron in green cane systems, under a heavy rainfall event of 120 mm that is becoming more frequent over the decades in tropical areas. A rainfall event of 80 mm h⁻¹ during 1.5 h was simulated over a 1 m² area, using a rainfall simulator with a structure designed to collect runoff. Herbicides in water runoff were determined by ultra performance liquid chromatography with mass spectrometry (UPLC ESI QTOF/MS), while herbicides attached to sediments were estimated using Kd values. Sugarcane straw on the soil surface decreased water, sediments, and diuron runoffs, but barely affected hexazinone losses. Crop residues cannot prevent runoff of highly soluble molecules, such as hexazinone. Herbicides’ runoffs were much higher in the aqueous phase and at higher soil moisture content. Maintaining 7 t ha⁻¹ of sugarcane straw on the soil surface was enough to mitigate water, sediments, and diuron runoff, but 3-day herbicide incubation did not affect both herbicides runoffs. Diuron and hexazinone are heavily used herbicides that can reach concerning concentrations in the runoff and contaminate surface waters in vulnerable areas if no control measures are taken.