Richness and density of aquatic benthic macroinvertebrates after exposure to fungicides and insecticides in rice paddy fields

ABSTRACT The objective of this study was to verify the richness and density of aquatic benthic macroinvertebrates after exposure to fungicides and insecticides of the rice paddy fields. In the crop seasons of 2012/13 and 2013/14, field experiments were performed, which consisted of single-dose applications of the fungicides trifloxystrobin + tebuconazole and tricyclazole, and the insecticides lambda-cyhalothrin + thiamethoxam and diflubenzuron, in 10 m2 experimental plots, over rice plants in the R3 stage. Control plots with and without rice plants were maintained in order to simulate a natural environment. Soil samples were collected during rice cultivation for assessment of the macroinvertebrate fauna. Chemical-physical parameters assessed in the experiments included temperature, pH and oxygen dissolved in the water and pesticide persistence in the water and in the soil. The application of a single dose of the pesticides and fungicides in the recommended period does not cause significant negative effects over the richness and density of the macroinvertebrates. Tebuconazole, tricyclazole and thiamethoxam showed high persistence in the irrigation water of rice paddy fields. Thus, the doses and number of applications of these products in crops should be carefully handled in order to avoid contamination of the environment.

Influence of agricultural land-use and pesticides on benthic macroinvertebrate assemblages in an agricultural river basin in southeast Brazil / Influência de pesticidas e uso da terra sobre as assembléias de macroinvertebrados bentônicos em uma bacia hidrográfica no Sudeste do Brasil

Land-use alterations and pesticide run-offs are among the main causes for impairment in agricultural areas. We evaluated the influence of different land-uses (forest, pasture and intensive agriculture) on the water quality and on benthic macroinvertebrate assemblages on three occasions: in the dry season, wet season and at the end of the wet season. Macroinvertebrates responded to this gradient of impairment: agricultural sites had significantly lower richness numbers than forested and pasture sites, and all major invertebrate groups were significantly affected. Most taxa found in forested sites were found in pasture sites, but often with lower densities. In this case, the loss of habitats due to sedimentation and the lower complexity of substrates seem to be the disruptive force for the macroinvertebrate fauna.

O desmatamento e o uso de pesticidas representam impactos importantes que ameaçam a integridade ambiental das áreas agrícolas. Neste estudo, foi avaliada a influência de diferentes usos do solo associados com atividades agrícolas (floresta, pastagem e agricultura intensiva) na qualidade da água e em comunidades de macroinvertebrados bentônicos em três ocasiões: estação seca, estação chuvosa e fim da estação chuvosa. A comunidade de macroinvertebrados bentônicos respondeu a esse gradiente de impacto: as áreas intensamente ocupadas por cultivos apresentaram uma riqueza significativamente menor do que as áreas florestadas e ocupadas por pastagens, com todos os grupos de macroinvertebrados sendo significativamente afetados. A maior parte dos táxons encontrados nas áreas de floresta foi registrada nas áreas de pastagem, mas sempre em menores densidades. Nesse caso, a redução de habitat em função da sedimentação e da menor heterogeneidade de substratos parece ser o principal impacto que ameaça a comunidade.

Impact of refined petroleum spills on water quality, macro-invertebrate and microbial communities of a tropical aquatic environment.

Water quality characteristics, benthic macro-invertebrates and microbial communities of three first order streams in South West Nigeria were investigated to assess the effects of refined petroleum five months after spillage. All physical and chemical conditions except temperature and pH were significantly different (P<0.01) at the upstream control stations and impacted stations reflecting the perturbational stress. The benthic macro-invertebrate fauna were dominated by arthropods, but the faunal spectrum was dissimilar at all the stations studied. Sampling stations at the epicentre of the spill showed considerable reduction in faunal compositions and relative abundance. Generally, the microbial density and diversity were highest in both soil and water samples from impacted sites than in control sites. There was a significantly higher proportion (P < 0.05) of hydrocarbon utilizers in soil than in water samples in all stations except in samples from stations (P<0.05).