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At least 379 records · Page 21Linked to original sources
PubMed1988

Effects of cadmium exposure on feeding of freshwater planktonic crustaceans.

1. Effects of cadmium exposure (0.010-0.100 ppm) on food consumption and assimilation rates of crustacean zooplankton from 2 lakes were studied in laboratory using radioisotope (14C) technique. 2. The inhibiting effects were significant 48 hr after Cd-exposure, but not after 20 hr exposure. 3. Daphnia spp. were the most affected cladocerans; copepods, especially the cyclopoids, appeared less sensitive. 4. The decrease in assimilation rates was much more marked than in the consumption rates. 5. The 14C-technique offers quick and sensitive means of studying the effects of heavy metal toxicity.

Animals↗
PubMed2000

Epilithic and planktonic leucine aminopeptidase activity and leucine assimilation along the River Tweed, Scottish Borders.

The microbial organic-nitrogen transformation variables, extracellular leucine aminopeptidase activity, and leucine assimilation, were determined at stone surfaces and in river water at six sites along 138 km of the River Tweed and also in a major tributary, the River Teviot. Sampling was on 3 days, representative of spring, summer and autumn. The variables, except for epilithic leucine assimilation, all showed significant downstream increase on at least 2 of the sampling days. Their values tended to be lowest in spring (early April). Aminopeptidase activity, leucine assimilation, microbial abundance, and pattern of downstream increase in the Tweed were shown to be broadly similar to in the River Swale, northern England. Microbial organic-nitrogen transformations and abundance in the Teviot tended to equal or exceed those in the lower Tweed, probably because of enrichment of the tributary by sewage-works discharges.

Animals↗
PubMed2001

Characterization of spirolides a, c, and 13-desmethyl c, new marine toxins isolated from toxic plankton and contaminated shellfish.

Three additional marine toxins, spirolides A (1), C (3), and 13-desmethyl-C (7), were isolated from contaminated scallops and phytoplankton collections obtained from a Nova Scotian aquaculture site, as well as from batch cultures of the dinoflagellate Alexandrium ostenfeldii obtained as a single-cell isolate from these phytoplankton assemblages. The structures of these new spirolide derivatives, characterized by mass spectrometry and NMR, indicate a close relationship with spirolides B (2) and D (4) isolated previously from contaminated shellfish in the same area. All of these compounds display "fast-acting" toxicity in the traditional bioassay used for monitoring shellfish, and this is related to the presence of a cyclic imine function in all these compounds. Those spirolides containing a vicinal dimethyl group in the seven-membered ring are resistant to oxalic acid hydrolysis, whereas those that do not are readily hydrolyzed. These observations suggest that the extra methyl group on the seven-membered imine ring of 3, 4, and 7 appears to block the process of imine hydrolysis perhaps by stereochemical interference.

Animals↗
PubMed2002

Effects of a mixture of two insecticides in freshwater microcosms: II. Responses of plankton and ecological risk assessment.

This paper reports on the chronic effects of a mixture of the insecticides chlorpyrifos and lindane in freshwater microcosms. Chronic treatment levels corresponding to concentrations of 0, 0.005, 0.01, 0.05, 0.1 and 0.5 times the LC50 of the most sensitive standard test organism were evaluated. The zooplankton community structure was altered from the 0.05 * LC50 treatment level upwards. Cladocerans were the most susceptible group, followed by Copepoda and Ostracoda. Rotifera increased in abundance at the higher treatment levels. Increased abundance of some phytoplankton taxa and increased chlorophyll-a levels were found at the two highest treatment levels, most probably a consequence of decreased grazing pressure. Threshold levels for the mixture, both at population and community/ecosystem level, corresponded well with those reported in the literature for the individual compounds. The overall risk assessment indicates no antagonistic or synergistic effects of the mixture at ecosystem level. It was found that the safety factors set by the Uniform Principles for individual compounds also ensure protection against chronic exposure to a mixture of insecticides at community level, though not always at species level.

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