Existing research about the impact of cattle breeding on water quality is limited, and there is a need for more extensive studies to provide a comprehensive understanding of the effects of these practices on water resources. Such analyses are crucial for assessing potential contaminants, identifying risks to aquatic ecosystems, and developing effective management strategies to ensure the sustainable coexistence of agriculture and water quality preservation.
In the three evaluated sites of the Doblado stream and in S3 A of Areco River, near the cattle breeding establishment, the DO was lower than the limit for protection of aquatic life (5.5 mg/L) (Ossana et al., 2016). This may be a consequence of the high organic matter content found in these sites. The decline in DO levels can be attributed to various factors, including human activities. Pollution from agricultural runoff, excessive nutrient inputs, high organic matter content, and the release of pollutants, as was the case for all water samples, can contribute to oxygen depletion in water bodies. Low DO levels in aquatic habitats pose a significant threat to aquatic life, especially amphibians (Cohen et al., 2012). These low levels impact their survival, growth, reproduction, behavior, and overall population dynamics. Moreover, DOC was high in all sites from Doblado stream. In water samples from S2 A of the Areco River and all samples from the Doblado stream, the DOC concentrations were higher than the average concentration of riverine DOC (10.4 mg/L) across the global rivers (Liu and Wang, 2022). The concentration of DOC in water bodies can have significant implications for the health and functioning of aquatic life. High concentrations of DOC can lead to imbalanced nutrient dynamics, potentially causing shifts in ecosystem productivity and composition (Creed et al., 2018). The decomposition of DOC by microorganisms consumes DO in water bodies, which can potentially lead to reduced DO levels. Also, DOC can act as a carrier for contaminants and pollutants in aquatic environments (Bhateria and Jain, 2016). Organic compounds present in DOC can form complexes with metals and other contaminants, affecting their bioavailability and transport (Yang et al., 2021). Consequently, high DOC concentrations can facilitate the spread and persistence of pollutants, potentially increasing their toxic effects on aquatic organisms. On the other hand, nitrates levels were higher in all sites from Areco river and can enter the environment through natural and anthropogenic sources such as animal farming, urban and agricultural runoff, industrial wastes (Camargo et al., 2005). The normal concentration of nitrates in freshwater ecosystems can vary depending on a range of factors such as geographical location, surrounding land use, hydrological conditions, and local nitrogen inputs. In water samples from the Areco River, the nitrate concentrations were similar to the previously reported in areas impacted by agricultural activities from Argentina (Andrade et al., 2021; Lutri et al., 2020). Also, phosphate plays a vital role in aquatic ecosystems. However, when present in elevated concentrations, can have significant impacts on freshwater ecosystems (Correll, 1998). In pristine rivers, annual loads of phosphorus to the river system are extremely low, since phosphorus is not abundantly available from the majority of natural geologies (Mainstone and Parr, 2002). In this case, in all water samples the levels of phosphate were similar or even higher than the reported in other agricultural areas from Argentina (Arreghini et al., 2005). Elevated nitrate and phosphate concentrations in freshwater ecosystems can lead to eutrophication, a process characterized by excessive nutrient enrichment and subsequent algal blooms and low DO levels (Correll, 1998).
The presence of metals in water bodies can have significant implications for aquatic life and ecosystem health. Metals are naturally occurring elements that can be found in water bodies through various processes, including the natural weathering of rocks, volcanic activity, however, there are some anthropogenic sources, such as the use of fertilizers and livestock feeds with metals in agricultural practices (Carnelo et al., 1997). In this study case, some metals exceeded the limit for protection of aquatic life, such as Cu in water samples from almost all sites (S2 A, S3 A, S1 D and S3 D). It can derive from human activities, such as industrial discharges, agricultural practices through the use of copper-based pesticides and fertilizers (Zhang et al., 2018). Furthermore, metal compounds, such as copper (Cu) and zinc (Zn), are extensively utilized in livestock production as essential supplements, playing a crucial role as trace elements necessary for the nutritional requirements of numerous animal species (Hejna et al., 2018). Additionally, these compounds are deliberately added to animal feed in higher concentrations to achieve supplementary beneficial effects (Rensing et al., 2018). The presence of Cu in aquatic ecosystems can have significant ecological implications. Particularly, the concentrations in water samples were similar or even higher than the 168 h-LC50 (19.5 µg/L) for R. arenarum embryos (Aronzon et al., 2011). Finally, Zn was higher than its limit (30 µg/L) mainly in all sites from the Doblado stream. Zinc is naturally present in rocks and minerals, including sphalerite (zinc sulfide). It can also enter the environment through the use of zinc-containing fertilizers, pesticides, dietary supplements for animals and animal manure in agricultural activities (Mortvedt and Gilkes, 1993). On the other hand, Mn also exceeded its corresponding limit mainly in the sites from the Doblado stream. Manganese can also derive from natural sources and/or through human activities, such as its use in manganese-based fertilizers (Kheirkhah et al., 2016). Vanadium was higher than the limit for protection of aquatic life in all sites from the Areco river. It also may come from natural sources. However, some industrial processes, such as metal smelting, and fossil fuel combustion can contribute to the release of V into the environment (Barceloux and Barceloux, 1999).
Pesticides, including herbicides, insecticides, and fungicides, can enter water bodies through various pathways such as runoff from agricultural fields, irrigation practices, and accidental spills (Akhtar et al., 2021). This contamination poses a significant threat to aquatic ecosystems. Pesticides can accumulate in sediments and persist for long periods, leading to chronic exposure for aquatic organisms. In this case, pesticides were detected in all sites, mainly in water samples rather than in sediments. Site 3 A presented the highest variability. In particular, 2,4-D was detected in water samples from all sites. The presence of 2,4-D in water bodies can have detrimental effects on aquatic ecosystems. Fish, amphibians, and aquatic plants may be directly exposed to the herbicide, leading to acute toxicity or sublethal effects (de Castro Marcato et al., 2017). Atrazine and its metabolites were also detected in all water samples. Atrazine is known to be a highly toxic endocrine disruptor to a wide range of aquatic organisms, including fish, amphibians, and invertebrates (Yang et al., 2021). Piperonyl butoxide was also detected in all water samples. It is a common pesticide synergist widely used in combination with insecticides to enhance their effectiveness and it is known to be toxic to aquatic organisms, including fish, invertebrates, and amphibians (Khan and Law, 2005). Tebuconazole, a commonly used systemic fungicide, was also detected in all water samples. Tebuconazole is also known to be toxic to aquatic organisms, including fish, invertebrates, and algae (Tofan et al., 2023). On the other hand, glyphosate, a widely used herbicide, and aminomethylphosphonic acid (AMPA), glyphosate´s degradation metabolite, were detected in all sediment samples. Both compounds can negatively affect sediment-dwelling organisms, such as amphibians’ larvae, which play essential roles in sediment health and nutrient cycling (Tresnakova et al., 2021).
Ivermectin was detected in all water and sediment samples. Studies have shown that IVM can remain active for extended periods in aquatic environments, leading to potential accumulation (Liebig et al., 2010; Suárez et al., 2022). Also, due to its physicochemical characteristics, it exhibits a strong attraction to sediment and organic matter, along with a limited ability to desorb and leach (Krogh et al., 2008), resulting in its quick transfer and long-term presence in the environment (Liebig et al., 2010). Its high persistence can result in adverse effects on aquatic organisms such as fish, invertebrates, and amphibians. A previous study reported a concentration of IVM of 1.24 µg/L in water from wetlands and a maximum concentration of 17.1 µg/kg in sediment (Mesa et al., 2020). Our study showed similar concentrations in water samples. However, in sediment samples our results were between 1.73 and 4.98 times higher. On the other hand, OTC, a commonly employed antibiotic in animal breeding, was detected in water and sediment samples near the cattle breeding establishments (S2A and S2D). Once in water bodies, OTC can persist for extended periods due to its low degradation rate (Lee et al., 2022). This persistence increases the likelihood of exposure for aquatic organisms. Oxytetracycline is known to have adverse effects on aquatic ecosystems, particularly on the microbial communities, algae, and aquatic invertebrates (Siedlewicz et al., 2020). Even though at higher concentrations than those reported in the present study, it has been shown that OTC can have negative effects on amphibians, particularly in R. arenarum larvae (Lourido et al., 2022). In a previous study (Peluso et al., 2023), we reported the first environmental concentrations of OTC in Argentina. However, in the current study, concentrations in both sediment and water were higher. This could be linked to an accumulation or a continuous input into the environment over time. Nevertheless, it could also be associated with a specific discharge or with changes in livestock load at the livestock facility.
Sediment testing serves as an initial indication of the toxicity of substances within this environmental compartment (Chapman, 2007). Field and laboratory studies are fundamental in identifying factors contributing to toxic effects. However, there is limited evidence regarding contamination in aquatic systems that integrates both water and sediment components as a complex entity. The exposed R. arenarum larvae exhibited lethal effects in all sites, during acute, sub-chronic and chronic exposure periods. Although some of the drugs, pesticides, and metals detected in the water samples were found at concentrations below the known lethal thresholds for R. arenarum larvae, as documented by previous studies (Brodeur et al., 2009; Sztrum et al., 2011), the toxic effects of most pesticides and metals on this particular species remain uncertain. It should be noted, that the concentrations of Cu in some sites were near the 168 h-LC50 reported for R. arenarum embryos (Aronzon et al., 2011). It is important to note that the observed lethality could result from complex interactions among multiple identified substances, including synergistic interactions such as between As and glyphosate (Lajmanovich et al., 2019), as well as 2,4-D and glyphosate (Peluso et al., 2022b). Moreover, it is crucial to highlight that the majority of the study sites caused lethality in organisms during extended exposure times. This finding emphasizes the significance of extending the duration of exposure when assessing the potential toxic effects of environmental samples. By extending the exposure times, a more comprehensive understanding of the cumulative and chronic impacts of the contaminants present on the samples is achieved (Luan et al., 2020). This approach enables a more accurate assessment of the long-term risks and helps to identify any delayed or sublethal effects that may not be apparent during shorter exposure periods.
The rise in trace element concentrations has become a significant concern in terms of environmental pollution, as these elements can be absorbed and incorporated by wildlife (Stankovic et al., 2014). Indeed, due to the high persistence and resistance to degradation of IVM, it tends to accumulate in aquatic environments (Mesa et al., 2020). Consequently, this persistence in aquatic systems can lead to prolonged exposure of amphibian larvae, potentially exacerbating its effects on them. The incorporation of IVM by amphibian larvae poses a great concern about its impacts on their development, survival, and overall fitness. Aquatic organisms can be exposed and incorporate IVM through the consumption of sediment particulate matter and the bioaccumulation of dissolved IVM (Mesa et al., 2020). In a previous study, it was observed that IVM was accumulated in aquatic communities within wetlands subjected to various cattle activities and differing frequencies of drug injection (Mesa et al., 2020). The larvae that survived the toxicity bioassays demonstrated evidence of IVM incorporation during the 504 h of exposure. However, no bioconcentration of this drug was observed at this exposure time, as the IVM concentrations in larvae were lower than those found in water samples. Nonetheless, due to their transition from aquatic to terrestrial environments, amphibians have the ability to transfer contaminants across diverse habitats. This capacity allows them to introduce these substances into the trophic chain, potentially leading to their incorporation and subsequent biomagnification throughout food webs. Consequently, this process has the potential to exert significant influences on the functionality of ecosystems (Mesa et al., 2020).
Exposure to all sediment and water samples only caused reduced GSH levels. Reduced glutathione (GSH) is a crucial antioxidant that protects cells from oxidative stress and maintains redox homeostasis (Ali et al., 2020). Exposure to stressors like habitat degradation, pollution, and diseases increases reactive oxygen species (ROS), causing oxidative stress. GSH serves as a first-line defense, neutralizing ROS and detoxifying harmful molecules. In amphibians, GSH levels serve as an important biomarker for overall health and response to stressors (Tsukada et al., 2023). Exposure to contaminants lowers GSH levels in amphibians, weakening their antioxidant defenses and increasing susceptibility to oxidative harm. In polluted habitats, amphibians frequently display reduced GSH levels, potentially compromising their ability to withstand oxidative stress and survive. This depletion of GSH due to contaminant exposure heightens amphibians' vulnerability to oxidative damage, potentially leading to negative impacts on their survival (Costa et al., 2008)
In recent years, researchers have noted a concerning decline in AChE and BChE activity in amphibians, raising questions about the potential ecological implications (Relyea, 2003). Pesticides, such as organophosphates and carbamates, are known to inhibit AChE and BChE activity, leading to neurotransmitter imbalances and impaired nervous system function (Nunes, 2011). However, in recent years, it has been reported that other compounds, such as metals and antibiotics, may alter AChE and/or BChE activity (Frasco et al., 2005a; Lourido et al., 2022). Agricultural runoff and direct applications of pesticides are major sources of contamination in amphibian habitats. A decrease in AChE and BChE activity disrupts the breakdown of acetylcholine, the primary neurotransmitter involved in neuromuscular function. This impairment can lead to muscle weakness, coordination deficits, and compromised motor control in amphibian (López et al., 2015). These effects may hinder their ability to forage, evade predators, and reproduce successfully. Consequently, their fitness may be reduced, which can lead to population decline and local extinctions.