The freshwater planarian Polycelis felina as a sensitive species to assess the long-term toxicity of ammonia

Behavioural endpoints are a good link between physiological and ecological effects. However long-term behavioural endpoints are not uniformly studied over all different organism groups. For example behaviour has been scarcely studied in planarians. Unionized ammonia (NH₃) is one of the most widespread pollutants in developed countries, and is known to alter animal behaviour. In this study a long-term (30 d) bioassay was conducted to assess the effect of this pollutant on survival and behavioural activity (e.g. locomotion activity) of the freshwater planarian Polycelis felina. One control and three environmentally-realistic concentrations of unionized ammonia (treatments of 0.02, 0.05, and 0.09 mg N-NH₃ L⁻¹) were used in quintuplicate. The behaviour of planarians was measured after 0, 10, 20 and 30 d of ammonia exposure. Mortality was recorded every 2 d. Unionized ammonia increased mortality in the two highest NH₃ concentrations and the locomotory activity was depressed in all treatments after 20 d of exposure. Behavioural effect was observed at concentrations 20 times lower than the short-term LC50 for this species. Previous studies proposed safe concentrations of unionized ammonia of 0.01-0.10 mg N-NH₃ L⁻¹ to aquatic ecosystems, but our study has shown that these concentrations will affect planarians. Because planarians play a key role in streams (as predator/scavenger), safe concentrations should be below 0.02 mg N-NH₃ L⁻¹ to protect this species in the freshwater community. Our results can contribute to improve the knowledge about ammonia toxicity to freshwater ecosystems, we recommend that safe concentrations of unionized ammonia should be based on very sensitive species.     

Mercury distribution in medium-size rivers and reservoirs of the Sao Paulo state (southeast Brazil)

The aim of this work was to investigate mercury (Hg) levels in six meso-scale watersheds (Upper Paranapanema, Aguapeí, Peixe, S?o José dos Dourados, Mogi-Gua?u, and Piracicaba) of the S?o Paulo state to contribute to a more comprehensive understanding of Hg contamination in Brazil. Water, sediment, bivalves, and fish samples were collected during 2001 at 11 sites. Fish were also collected in the Jurumirim and Salto Grande Reservoirs which are 39 and 52 yr old since impoundment, respectively. Results showed that Hg concentrations were low in almost all samples, except fish from Jurumirim Reservoir (total mercury [T-Hg] = 1.14 +/- 0.55 mg kg(-1) wet wt.). In spite of industrialization and high population, the results showed that there was no important source of Hg contamination in the investigated areas. The higher concentrations found in fish from Jurumirim seem to be the result of processes that favor Hg mobilization and methylation as a consequence of the impoundment of the reservoir area. The same levels were not observed in the Salto Grande Reservoir, probably because these are no longer significant due to the long time since the impoundment. To understand the dynamics of methylmercury (MeHg) production and its accumulation in fish, further studies are needed in the Jurumirim Reservoir. The results show that even at low T-Hg concentrations in sediment and water, concentrations in fish can reach values that pose concerns for consumption. This emphasizes the importance of designing an optimized biomonitoring program that can provide warning of biogeochemical conditions that promote formation of MeHg.     

Resistant weeds were controlled by the combined use of herbicides and bioherbicides

The intensive and abundant use of synthetic herbicides has been questioned in recent decades due to the strong dependence and also the resistance effects that are identified in weeds. Several grain crops suffer from the weed control system because many of the weeds are already resistant to the main herbicides that are used. In recent years, there has been a large gap in the market without the addition of new synthetic herbicides with mechanisms of action that differ from those already existing. The objective of this short piece is to address and overcome this challenge and bring an innovative and alternative solution that proposes a synergistic action system between bioherbicides produced by the fungus Trichoderma koningiopsis and synthetic herbicides (2,4‐dichlorophenoxyacetic acid, glyphosate, and ammonium glufosinate). The plants included in this study were Bidens pilosa (amor seco, or in the United States, beggar ticks or Spanish needle), Euphorbia heterophylla (adeus‐brasil), and Conyza bonariensis (margaridinha‐do‐campo, or, in the United States, hairy fleabane or asthmaweed). It was verified that, in the application of the biocomposites in the presence of chemical herbicides, potentiation of the phytotoxic action (100%) occurred under the target plants, emphasizing phytotoxicity to the weed, C. bonariensis, which is currently resistant to available herbicides. The bioherbicides studied have promising characteristics to be explored in the biocontrol of weeds.     

Nitrate causes deleterious effects on the behaviour and reproduction of the aquatic snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca)

Nitrate (NO₃ ^?) is present in aquatic ecosystems as a natural component of the nitrogen cycle. However, in the last decades, several human activities are the causes of the rising amounts of organic matter and inorganic nitrogen nutrients in aquatic ecosystems, causing notable increase of nitrate above background natural levels. In spite of the toxicity of nitrate to aquatic animals, there are relatively few studies on the chronic toxicity of this compound to invertebrates. The aim of our study is to assess the effect of chronic (35 days) exposure to nitrate on the behaviour (velocity of movement) and reproduction (number of newborns) of the aquatic snail Potamopyrgus antipodarum. Four actual concentrations of nitrate were used (21.4, 44.9, 81.8 and 156.1 mg?N-NO₃ ^?/L). In each treatment, 12 animals were individually monitored for velocity (weekly) and newborn production (every 3–4 days). Velocity was recorded using quantitative video monitoring. Our results showed that nitrate did not cause mortality, but it reduced the velocity of movement (at 44.9, 81.8 and 156.1 mg?N-NO₃ ^?/L) and number of live newborns (in all tested concentrations). Reproductive impairment was caused at realistic nitrate concentrations which is relevant to the risk assessment of this compound. Our study contributes to the knowledge of the chronic effects of nitrate on the behaviour and reproduction of an aquatic snail.