Chromium bioavailability in aquatic systems impacted by tannery wastewaters. Part 1: Understanding chromium accumulation by indigenous chironomids.

The tanning industry uses large quantities of Cr whose contribution to the contaminant burden of aquatic organisms is not yet fully understood. The present study investigated Cr bioaccumulation by indigenous chironomids in a freshwater ecosystem impacted by tannery effluents. Total Cr content in sediments and in chironomids was determined on several occasions. Chromium distribution among sediments and pore waters, and Cr speciation in overlying and pore waters were studied in detail to understand possible factors controlling Cr bioavailability to chironomids. Total chromium concentration ranged from 69 to over 3000 µg g-1 dry weight in sediments and from negligible to over 300 µg g-1 dry weight in chironomids (values corrected for sediment gut content). Filterable (<0.45 µm) Cr concentration in overlying waters and pore waters from the surface sediment layers (upper 2 cm) ranged from 3 to 120 µg L-1, with Cr(VI) representing 0.5-28% of the total filterable Cr. Chromium profiles in pore waters as determined by diffusive equilibration in thin films (DET) and diffusive gradient in thin films (DGT) were comparable. DGT-labile Cr accounted for <2% of the total Cr measured by DET. Although Cr concentrations in sedimentary and aqueous matrices were not directly proportional to Cr levels measured in chironomids, the available findings suggested that Cr inputs from tanneries were bioavailable to resident chironomids. These observations are of particular importance considering that Cr(III), putatively of limited bioavailability and ecotoxicological concern, is the predominant redox form of Cr in bed sediments impacted by tannery discharges. The companion paper provides further insight into Cr bioavailability and effects in tannery impacted ecosystems using a combination of in situ and laboratory approaches.

Cytotaxonomic characteristics of the genus Glyptotendipes Kieffer (Chironomidae, Diptera) from fish and retention ponds (Silesia, southern Poland).

The cytotaxonomic characteristics of species of the genus Glyptotendipes (Chironomidae): G. glaucus Meigen, G. paripes Edwards, and G. barbipes (Staeger) are described. The studied material was collected from a fish pond at Golysz and a sewage retention pond at Chybie in Silesia. All the studied species have the chromosome set 2n = 8, but with many specific structural and functional changes. The cytogenetic data of G. glaucus showed that the studied specimens of this species have been produced by the introgressive hybridization of two sibling species: G. glaucus x G. pallens, and subsequent crossing-over in the hybrid chromosome CD. Owing to this process, the band pattern of chromosome arm D coincided with those of G. pallens. New aberrations (homo- and heterozygous deletions in arm G as well as heterozygous inversions in chromosome arm B) were detected in G. glaucus. Specific band sequences were discovered in chromosomes of G. paripes. The band patterns established in chromosomes AB and G of this species were identical with those of Siberian populations. The banding patterns of the polytene chromosomes of G. barbipes do not differ from the standard. However, high frequency of pericentric inversion of chromosome AB was established. Many new puffs were found in the polytene chromosomes of all the studied species. Their nucleolar organizer was very sensitive to environmental changes. In G. glaucus it appeared in three different states: very active, slightly active, and heterozygous state. The organic pollution existing in the sewage retention pond may contribute to possible mutations and chromosomal damage in Glypotendipes species. Structural and functional rearrangements of the polytene chromosomes of these species mobilized their genomes and provide for survival under polluted conditions.

The pharmacokinetics, pharmacological responses and behavioral effects of acepromazine in the horse.

After intravenous (i.v.) injection, acepromazine was distributed widely in the horse (Vd = 6.6 litres/kg) and bound extensively (greater than 99%) plasma proteins. Plasma levels of drug declined with an alpha half-life of 4.2 min, while the beta phase or elimination half-life was 184.8 min. At a dosage level of 0.3 mg/kg acepromazine was detectable in the plasma for 8 h post dosing. The whole blood partitioning of acepromazine was 46% in the plasma phase and 54% in the erythrocyte phase. Penile prolapse was clearly evident at doses from 0.01 mg/kg to 0.4 mg/kg i.v., and the duration and extent of protrusion were dose related. Hematocrit levels were significantly lowered by administration of 0.002 mg/kg i.v. (about 1 mg to a 500 kg horse) and increasing dosages resulted in greater than 20% lowering of the hematocrit from control levels. Pretreatment of horses with acepromazine also reduced the variable interval (VI 60) responding rate in all horses tested. These data show that hematocrit changes are the most sensitive pharmacological responses to acepromazine, followed by changes in penile extension, respiratory rate, VI responding and locomotor responses. Acepromazine is difficult to detect in plasma at normal clinical doses. However, because of its large volume of distribution, its urinary elimination is likely prolonged, and further work on its elimination in equine urine is required.

Pharmacokinetics and behavioral effects of methylphenidate in Thoroughbred horses.

In horses given (rapid IV) methylphenidate (Ritalin, alpha-phenyl-2-piperidinacetic acid methyl ester; 0.70 mg/kg), plasma concentrations of the drug decreased rapidly at first, with an apparent alpha half-life of about 19 minutes, and then more slowly, with an apparent beta half-life of about 2.4 hours. These data were well fitted by a 2-compartment open model. In blood, about 40% of the methylphenidate present was in the plasma fraction, and of this, about 80% was plasma-protein bound. If given by subcutaneous or IM injection, plasma concentrations of methylphenidate peaked in about 1 hour and were no longer detectable (cleared) from plasma by 6 hours. Urinary clearance time, however, was longer, and between 12 and 24 hours should be allowed for a dose of methylphenidate to "clear" from urine. Using a variable-interval responding apparatus, methylphenidate was shown to stimulate the responding rate of horses up to 6 times above base line, making it the most potent central stimulant tested in this responding apparatus to date. Peak central stimulation at 30 minutes after IV dosing was seen in horses given 0.4 to 1.0 mg of methylphenidate/kg.