The aim of this research is to describe the impact of heavy metals contaminating sediments on oligochaete communities. Sediments were collected three times (June, August, October 1991) for chemical and biological analyses in 15 sites situated in the river I11 and its tributaries (Rhine Basin, France). The sediments are characterized by high contents of heavy metals, mainly Hg, Cu, Cr, Pb, Zn from below the city of Mulhouse. The majority of sediments are heavily loaded with organic matter and organic micropollutants are also present. Oligochaete communities are rich in species. However five species only, considered as pollution-tolerant or opportunist, are significantly present and abundant. The percentages of Tubificidae without hair setae are positively related to heavy metal contents of the sediments, and the percentages of Tubificidae with hair setae are negatively related. Several species such as N. communis, N. barbata, D. digitata and Bothrioneurum sp. are considered as tolerant to heavy metals; on the contrary L. claparedeanus, L. udekemianus, Stylodrilus sp. and S. josinae are considered as intolerant. The reproductive strategy of oligochaetes in contaminated areas and the role of organic matter are discussed. Several recommendations are given for the rehabilitation of the investigated sites.
.).Generally, a high content of heavy metals is associated with low values of the oligochaete biotic index IOBS (IOBS ^ 1) and low abundances of worms (^ 1 000 worms . 0.1 m -2 ). Furthermore, the percentages of Tubificidae without hair setae are positively related to heavy metal content of the sediments and the percentages of Tubificidae with hair setae are negatively related. Moreover, the sexual reproduction of oligochaetes seems to be inhibited by heavy metals : the adults of Tubificidae worms seem to be less tolerant than their immatures and the data suggest that asexual reproduction might be a strategy of tolerance to heavy metal contamination.
Magnesium balance, and plasma and urinary levels, were studied in spontaneously hypertensive (SHR), Wistar Kyoto (WKY) and in Wistar (WI) rats. We found few differences in the measured parameters between WKY and WI rats, but the SHR rat which similarly maintained Mg balance has lower plasma Mg levels and less urinary Mg excretion. These abnormalities could favor establishment or maintenance of hypertension.
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