Chromate ion as a reference toxicant for aquatic phytotoxicity tests

Abstract

To conduct toxicity tests, it is essential to include controls to ascertain the health of the test organisms. The common practice is to include negative controls in every test. That positive controls are not used is perhaps because there is no consensus about the reference toxicant. The objective of this study was to test chromate ion as a candidate for reference toxicant. Two aquatic phytotoxicity tests were performed: a millet root elongation test and a duckweed test. To the same test species, the Cr(VI) toxic effect was very consistent in repeated experiments. The toxic effects to millet were nearly identical in both deionized water and sewage effluent samples. The toxic effect to duckweed was also highly repeatable in 59 water samples from 18 sample stations. The results suggest that the Cr(VI) ion can be used as a general reference toxicant in river water, lake water or wastewater samples. The concentration‐effect relationships, however, are different, depending on the test organisms.

Assessment of Lake Orta sediments phytotoxicity after the liming treatment

“…For the seed germination and root elongation tests, seeds of the common lettuce (Lactuca sativa) were used, following the method described by Wang (1987a). For each experiment, 4 ml of pore water were added to a polystyrene Petri dish (60 × 10 mm) containing a Whatman No.…”

“…Results were evaluated with respect to control charts based on tests with two reference toxicants, K 2 Cr 2 O 7 and Cu(NO 3 ) 2 , as suggested by Wang (1987a). These positive controls were considered appropriate because of the very high concentrations of chromium and copper in Lake Orta sediments (Baudo & Beltrami 2000).…”

“…Suggested plant species include cucumber, lettuce, radish, red clover, and several varieties of wheat (Brusick & Young 1981;Ratsch 1983;OECD 1984;Fletcher et al 1985;Wang 1987a;Wang & Williams 1988). Other candidate species include oats, corn, cabbage, carrots, soybeans, tomatoes, ryegrass, onions, and beans (U.S. Food and Drug Administration 1984; US EPA 1996), as well as rice, sorghum, mustard, rapeseed, turnip, vetch, fenugreek, and cress (OECD 1984).…”

Test System Stability and Natural Variability of a Lemna Gibba L. Bioassay

“…The phenomenon of seasonally altered duckweed growth (under constant laboratory conditions) has also been observed elsewhere. Based on the number of fronds Wang [24] suggested a seasonal variation in the growth of L. minor . Pirson et al [31] described annual rhythmic changes in root growth of L. minor under controlled conditions, while Bornkamm [32] reported for the same duckweed species seasonal changes in the rate of dry matter production and the protein/carbohydrate ratio, which seemed to correspond to periodic changes of a field population.…”

“…In addition, for appropriate interpretation of the results from a set of experiments conducted over a longer time span, it is also essential to know the variability range of the experimental set-up over this period. Duckweeds, like all living organisms, may exhibit considerable variations in their growth and metabolic activity over time even under controlled laboratory conditions [23] , [24] . Endogeneous rhythms have been described even on a molecular level [7] .…”