Contact Toxicity of Metals in Sewage Sludge: Evaluation of Alternatives to Sodium Chloride in the Microtox® Assay

Abstract

The presence of chloride ions in the Microtox@ test can cause problems when testing metal toxicity, both due to extraction of metals from solid samples and formation of chloro complexes of metals in the liquid phase. To investigate alternatives to NaCl in the Microtox test, the toxicity of Cu, Cd, Pb, and Zn to Photobactertumphosphoreum was tested in 28 osmotic surrogates for NaCI. It was found that Na+ must be present to keep the blank luminescence stable for 30 min. The results point to NaC10, as the most satisfactory surrogate solution as it has an inert behaviour and does not form complexes with any metal of environmental interest. Raw, digested, and reference sewage sludges were tested in the osmotic surrogates. The EC50 values for sludges were lower in solutions of NaNO,, Na,SO,, and NaCIO,, and higher in sucrose, mannitol, and KCI, compared to NaC1. NaCIO, can be recommended as an osmotic surrogate for sewage sludge testing. Another problem with the Microtox assay is the lack of pH control in the cuvette. Copper toxicity tests were carried out in Tris buffer and KH2P04 at two different concentrations and at pH 7 and 8. The results show that 1 mM phosphate buffer, pH 7.0, can be recommended for solid samples. However, owing to formation of KCIO, a buffer containing potassium is not recommended in combination with NaC10,.

Assessment of mixture toxicity of copper, cadmium, and phenanthrenequinone to the marine bacterium Vibrio fischeri

“…It strongly affects enzyme systems and essential cellular metabolism (Chang et al, 1996;Achard-Joris et al, 2007). The EC 50 s of Cu in different studies with V. fischeri range from 100 to 170 lg/ L after 30 min of exposure (Carlsonekvall and Morrison, 1995;Newman and McCloskey, 1996;Utgikar et al, 2004). The 30 min EC 50 of 146 lg/L, determined in this study, is in agreement with those reports.…”

“…Transition metals such as Cu and Cd, and oxyPAHs such as PHQ, frequently occur in the environment as cocontaminants (Mowat and Bundy, 2002). Although there is information on the individual effects of these three chemicals on V. fischeri (Carlsonekvall and Morrison, 1995;Villaescusa et al, 1996;McConkey et al, 1997;El-Alawi et al, 2002b;Mowat and Bundy, 2002), studies that examine the effects of Cu/PHQ or Cd/PHQ mixtures on this bioluminescent bacterium have not been performed. In the present study, the cotoxicity of Cu/PHQ was found to be dependent on the mixture ratio.…”

Influence of Complexation With Chloride on the Responses of a Lux- Marked Bacteria Bioassay to Cadmium, Copper, Lead, and Mercury

“…The chloride concentration (and thus ionic strength or salinity) of a sample is an important factor in microbial bioassays because it affects the luminescence output of the biosensor directly and the speciation of heavy metals. The latter effect has previously been highlighted as a potential problem with standard Microtox assays [1,2,6,7]. We have clearly shown here that the response of E. coli to heavy metals may vary significantly even at low salinities.…”

“…The merits of bioassays using naturally occurring bioluminescent organisms for ecotoxicity testing are well established with the marine organism Vibrio fischeri, which is extensively used in the standard Microtox assay (Microbics, Carlsbad, CA, USA). However, this biosensor, although sensitive, needs to be used in a highly saline matrix (2% w/v), which may lead to the formation of chloride complexes for the metal under test [1,2]. Bioavailability (and thus toxicological response) is directly affected by chemical speciation.…”

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][31][32][33][34][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.…”