RESUMO
Aquatic ecosystems of the Bolivian Altiplano (â¼3800 m a.s.l.) are characterized by extreme hydro-climatic constrains (e.g., high UV-radiations and low oxygen) and are under the pressure of increasing anthropogenic activities, unregulated mining, agricultural and urban development. We report here a complete inventory of mercury (Hg) levels and speciation in the water column, atmosphere, sediment and key sentinel organisms (i.e., plankton, fish and birds) of two endorheic Lakes of the same watershed differing with respect to their size, eutrophication and contamination levels. Total Hg (THg) and monomethylmercury (MMHg) concentrations in filtered water and sediment of Lake Titicaca are in the lowest range of reported levels in other large lakes worldwide. Downstream, Hg levels are 3-10 times higher in the shallow eutrophic Lake Uru-Uru than in Lake Titicaca due to high Hg inputs from the surrounding mining region. High percentages of MMHg were found in the filtered and unfiltered water rising up from <1 to â¼50% THg from the oligo/hetero-trophic Lake Titicaca to the eutrophic Lake Uru-Uru. Such high %MMHg is explained by a high in situ MMHg production in relation to the sulfate rich substrate, the low oxygen levels of the water column, and the stabilization of MMHg due to abundant ligands present in these alkaline waters. Differences in MMHg concentrations in water and sediments compartments between Lake Titicaca and Uru-Uru were found to mirror the offset in MMHg levels that also exist in their respective food webs. This suggests that in situ MMHg baseline production is likely the main factor controlling MMHg levels in fish species consumed by the local population. Finally, the increase of anthropogenic pressure in Lake Titicaca may probably enhance eutrophication processes which favor MMHg production and thus accumulation in water and biota.
Assuntos
Monitoramento Ambiental , Lagos/química , Mercúrio/análise , Poluentes Químicos da Água/análise , Animais , Bolívia , Ecossistema , Eutrofização , Peixes , Cadeia Alimentar , Mineração , PlânctonRESUMO
In this study, historical data available since 1954 were used to get new insight to ontogenetic and spatiotemporal variability in Peruvian anchovy or anchoveta Engraulis ringens diet. Whatever the period, E. ringens foraged mainly on macrozooplankton and the importance of euphausiids in E. ringens diet appears directly related to euphausiids abundance. This bottom-up effect is also observed at smaller scale because the euphausiids fraction increased with E. ringens total length and euphausiids accessibility. Selecting the largest prey, the euphausiids, provides an energetic advantage for E. ringens in its ecosystem where oxygen depletion imposes strong metabolic constraints on pelagic fishes. This study illustrates the plasticity of E. ringens that allows it to cope with its highly variable environment.
Assuntos
Dieta/veterinária , Peixes/fisiologia , Cadeia Alimentar , Animais , Peru , Análise Espaço-TemporalRESUMO
OBJECTIVE: To analyze the clinical and histological findings in boys with bilateral anorchia and the response to testosterone treatment on penis length. STUDY DESIGN: Patients were divided into two groups according to the absence (group A, n = 29) or the presence (group B, n = 26) of palpable intrascrotal or inguinal mass at first clinical examination. RESULTS: A micropenis was found in 46% of patients (n = 24) with a similar proportion in both groups. Testosterone treatment induced a mean penis length gain of 1.9 +/- 1.3 SDS (standard deviation score). However, micropenis persisted in six patients. Histological examination (n = 18) confirmed the absence of any testicular structure with deferent ducts being present unilaterally or bilaterally in all but three patients. In these three patients, a hemorrhagic testis, probably as a result of a mechanical torsion, was found. CONCLUSIONS: The presence of isolated micropenis in almost half of patients with bilateral anorchia strongly suggests that the testicular damage frequently occurs during the second half of gestation after male sexual differentiation. In most cases, testosterone treatment stimulates the penile growth. Although the pathogenesis of bilateral anorchia may be heterogeneous, our study suggests that gonads may have been functionally abnormal before they disappeared, and suggests that some patients have an intrinsic endocrine disorder.