Evaluation of Sucrose as an Alternative to Sodium Chloride in the Microtox® Assay: Comparison to Fish and Cladoceran Tests With Freshwater Effluents

Abstract

The toxicity of 44 freshwater effluents was evaluated using the fathead minnow (Pimephules promelas), a cladoceran (Ceriodaphniu dubia) and Microtoxa (Photobacterium phosphoreum). The latter assay was conducted with both sodium chloride (NaC1) and sucrose for osmotic protection of the bacteria in an effort to determine whether the use of sucrose increased the sensitivity of Microtox to samples exhibiting toxicity to the fish and cladoceran species. Twenty-three of the effluents tested were toxic to fathead minnows and/or C. dubia; of these, Microtox was sensitive to 10 when tested in NaCl and seven when tested in sucrose. In one instance testing in sucrose predicted toxicity to the fish and cladoceran species when testing in NaCl did not. Single chemical tests demonstrated that Microtox sensitivity was greater to zinc chloride, nickel chloride and methanol when tested in sucrose as opposed to NaCI, about equal to copper sulfate and phenol in sucrose and NaC1, and was far greater to chlorine when tested in NaCl than in sucrose. These results, as well as data from Microtox assays with effluents containing known toxicants, suggest that the use of sucrose, in conjunction with NaC1, for osmotic adjustment in the assay could be helpful as part of a suite of tests for identifying general classes of compounds responsible for toxicity in freshwater effluents.

Evaluation of a Bacterial Bioluminescence Bioassay as a Predictive Surrogate for Mysid Chronic Estimator Tests With Produced Water

“…(2, 4). Other studies have shown poor correlation (13,14) with high proportions of false negatives, where Vi6rio does not demonstrate toxicity seen in the standard species.…”

Sensitivity and Significance of Luminescent Bacteria in Chronic Toxicity Testing Based on Growth and Bioluminescence

“…This fact must be connected with the addition of NaCl as osmotic regulator. The saline milieu is responsible for the higher tolerance to Cd>, Pb>, and Cu> (Carlson-Ekvall et al, 1995) and to Zn> (Ankley et al, 1990). Also, the sample pH adjustment to a neutral range, which is part of the test preparation, may have contributed to the detection of toxicity at a lower level.…”

Influence of salinity on Vibrio fischeri and lux‐modified Pseudomonas fluorescens toxicity bioassays

“…Previous studies have shown salinity to have a protective effect on bioassay organisms; chloride can form relatively nontoxic complexes with metal contamination and mitigate the toxic effect of metals [8,11,17,22,30–35]. This effect is exhibited over low ranges of salinity, where metals are ionic (i.e., most toxic) in the absence of salinity, and complexation with chloride increases with increased salinity, reducing toxicity of the metal.…”

“…The use of an alternate osmotic adjustment compound, sucrose, has been investigated by several researchers in an attempt to reduce chemical changes in the test solution by complexation with metals. However, use of sucrose decreases the toxicity of some metals and increases the toxicity of others and has also been shown to affect the toxicity of organic compounds that are not expected to complex with chloride ions [11,36]. The results of Microtox tests performed with sucrose do not correlate well with NaCl adjusted results, and sucrose adjustment of samples is not recommended as a replacement for NaCl adjustment during routine analysis [3,11].…”

“…The effective concentration of chemical or test sample causing a 50% inhibition of light (EC50) after a specified period of time (e.g., 15 min) is reported [3]. Use of the Microtox bioassay has been extensive and has included evaluation of many chemicals in aqueous solution [4–8], contaminated groundwaters and wastewaters [9–12], and aqueous and organic extracts of contaminated soils and sediments [13–16].…”