Toxicity of mixtures of aquatic contaminants using the luminescent bacteria bioassay

Evaluation of the acute effects of chemical additives on the toxicity of a synthetic oilfield produced water

This study evaluated the acute effects of nine different production chemicals typically employed in oil exploration on the toxicity of a synthetic produced water (PW). Bioassays with the Microtox® System were performed to monitor changes in the level of light emission of the marine luminescent bacteria Vibrio fischeri during exposure to the samples. The results show that synthetic PW is moderately toxic to these organisms, and the addition of oilfield chemicals significantly increases its toxicity. For most of the additives tested, the toxicity of the aqueous phase following partitioning against crude oil was not strongly altered by the presence of these chemicals. Synergistic effects occurred in the three different mixtures investigated. Among the additives studied, biocide, corrosion inhibitor, H₂S scavenger, and surfactant were the most toxic for V. fischeri. Furthermore, the surfactant has been identified as the possible source of the acute toxicity observed.

Mathematical Modeling Approaches for Assessing the Joint Toxicity of Chemical Mixtures Based on Luminescent Bacteria: A Systematic Review

Developments in industrial applications inevitably accelerate the discharge of enormous substances into the environment, whereas multi-component mixtures commonly cause joint toxicity which is distinct from the simple sum of independent effect. Thus, ecotoxicological assessment, by luminescent bioassays has recently brought increasing attention to overcome the environmental risks. Based on the above viewpoint, this review included a brief introduction to the occurrence and characteristics of toxic bioassay based on the luminescent bacteria. In order to assess the environmental risk of mixtures, a series of models for the prediction of the joint effect of multi-component mixtures have been summarized and discussed in-depth. Among them, Quantitative Structure-Activity Relationship (QSAR) method which was widely applied in silico has been described in detail. Furthermore, the reported potential mechanisms of joint toxicity on the luminescent bacteria were also overviewed, including the Trojan-horse type mechanism, funnel hypothesis, and fishing hypothesis. The future perspectives toward the development and application of toxicity assessment based on luminescent bacteria were proposed.

Interactions of Cd, Cr, Pb, Ni, and Hg in their effects on activated sludge bacteria by using two analytical methods

Since trace metals rarely appear singly in industrial effluents, it is a major challenge to address combined effects of such toxicants on biological units of wastewater treatment plants. The aim of this study was interaction assessment of Cd, Cr, Pb, Ni, and Hg in their effects on activated sludge bacteria using analytical methods. Two mathematical models were used to determine the effect of binary mixtures of Hg, Cd, Cr, Pb, and Ni on activated sludge bacteria using a dehydrogenase enzyme assay. Calculated EC₅₀ values were compared to experimentally observed values of mixtures. Interactive effects were counted to be antagonistic for Hg and Cd, Cd and Pb, Cd and Ni, and Cr and Pb, synergistic for Cd and Cr and Hg and Cr, and additive for other binary mixtures. Maximum toxicity was related to Hg and Cr, Cd and Cr, and Hg and Cd. Physicochemical monitoring of single metals may underestimate hazards arising from these pollutants in environmental samples. Therefore, any possible interaction between metals in such environments should be considered when establishing environmental safety standards.

Phytoremediation of water polluted by thallium, cadmium, zinc, and lead with the use of macrophyte Callitriche cophocarpa

The objective of the present work was to study the phytoremediation capacity of Callitriche cophocarpa concerning water contaminated with thallium (Tl), cadmium (Cd), zinc (Zn), and lead (Pb) derived from the natural environment. We found that after a 10-day incubation period, shoots of C. cophocarpa effectively biofiltrated the water so that it met (for Cd, Zn, and Pb) appropriate quality standards. The order of accumulation of the investigated elements by shoots (mg kg(-1) dry weight) were as follows: Zn (1120) < Tl (251) < Cd (71) < Pb (35). The order of bioconcentration factors were as follows: Cd (1177) < Tl (1043) < Zn (718) < Pb (597). According to Microtox bioassay, C. cophocarpa significantly eradicated polluted water toxicity. During the experiment, the physiological status of plants was monitored by taking measurements of photosystem II activity (maximum efficiency of PSII, photochemical fluorescence quenching, nonphotochemical fluorescence quenching, and quantum efficiency of PSII), photosynthetic pigment contents, and shoot morphology. Plants exposed to metallic pollution did not exhibit significant changes in their physiological status compared with the control. This work is potentially applicable to the future use of C. cophocarpa in the phytoremediation of polluted, natural watercourses.

Assessment of respiration activity and ecotoxicity of composts containing biopolymers

The research was conducted to determine if introducing biodegradable polymer materials to the composting process would affect selected biological properties of mature compost. Determination of biological properties of composts composed of testing their respiration activity and toxicity. Respiration activity was measured in material from the composting process by means of OxiTop Control measuring system. The ecotoxicity of composts was estimated by means of a set of biotests composed of three microbiotests using five test organisms. Introduction of polymer materials caused a decrease in respiration activity of mature compost. Similar dependencies as in the case of mass loss were registered. Compost to which a biodegradable polymer with the highest content of starch was added revealed the smallest difference in comparison with organic material composted without polymers. Lower content of starch in a polymer caused lower respiration activity of composts, whereas microorganism vaccine might have accelerated maturing of composts, thus contributing to the smallest respiration of compost. In composts containing biopolymers the following were observed: an increase in germination inhibition--2.5 times, roots growth inhibition--1.8 times, growth inhibition of Heterocypris incongruens--four times and luminescence inhibition of Vibrio fischeri--1.6 times in comparison with the control (compost K1). Composts containing biopolymers were classified as toxicity class III, whereas the compost without polymer addition as class II.

Study on the toxicity of binary equitoxic mixtures of metals using the luminescent bacteria Vibrio fischeri as a biological target

Results from two mathematical approaches to predict the toxicity of all the possible binary equitoxic mixtures of Co, Cd, Cu, Zn and Pb were compared to the observed toxicity of these mixtures to Vibrio fischeri bacteria. Combined effect of the metals was found to be antagonistic for Co-Cd, Cd-Zn, Cd-Pb and Cu-Pb, synergistic for Co-Cu and Zn-Pb and merely additive in other cases, revealing a complex pattern of possible interactions. Besides, Cd appears much less toxic to the bacterial model than to animal cells. The synergistic effect of the Co-Cu combination and the strong lowering of Pb toxicity in the presence of Cd deserve much attention when establishing environmental safety regulations.

Toxicity of metals and metal mixtures: analysis of concentration and time dependence for zinc and copper

The toxic effects of heavy metals, zinc and copper, in unary and binary solutions were studied using the Microtox acute toxicity test which relies upon the attenuation of light intensity emitted by Vibrio fischeri. The toxic effect Gamma (ratio of the light intensity lost at time t to the light intensity remaining at time t) of zinc could be related to its concentration [X] by a two-parameter equation Gamma=a(1-exp(-b[X])), where parameter a was a function of time and b equal to 0.88L/mg. The toxic effect of zinc asymptotically approached a maximum with respect of to concentration at all times. The toxic effect of copper was fundamentally different from that of zinc, and increased exponentially with concentration without any limiting maximum value. It could also be described by a two-parameter equation, however, the equation had the form Gamma=aexp(b[X]), where parameter a was a constant and b a function of time. The different functional dependencies (of the toxic effect on the metal concentration) of zinc and copper indicate that different toxicity/inhibition mechanisms were possibly responsible for the attenuation of light intensity for the two metals. The toxic effects of binary mixtures were substantially higher than those expected on the basis of additivity of individual metals. No simple correlations were obtained that could relate the toxic effect of binary mixture to those of individual metals. A better understanding of metal-microbe interactions is needed for achieving predictive capability for toxic effect of mixtures.

The comparison of rapid bioassays for the assessment of urban groundwater quality

Groundwater is a complex mixture of chemicals that is naturally variable. Current legislation in the UK requires that groundwater quality and the degree of contamination are assessed using chemical methods. Such methods do not consider the synergistic or antagonistic interactions that may affect the bioavailability and toxicity of pollutants in the environment. Bioassays are a method for assessing the toxic impact of whole groundwater samples on the environment. Three rapid bioassays, Eclox, Microtox and ToxAlert, and a Daphnia magna 48-h immobilisation test were used to assess groundwater quality from sites with a wide range of historical uses. Eclox responses indicated that the test was very sensitive to changes in groundwater chemistry; 77% of the results had a percentage inhibition greater than 90%. ToxAlert, although suitable for monitoring changes in water quality under laboratory conditions, produced highly variable results due to fluctuations in temperature and the chemical composition of the samples. Microtox produced replicable results that correlated with those from D. magna tests.

Use of bacterial biosensors to interpret the toxicity and mixture toxicity of herbicides in freshwater

The dose response relationship between seven commonly used herbicides and four luminescence-based bacterial biosensors was characterised. As herbicide concentration increased the light emitted by the test organism declined in a concentration dependent manner. These dose responses were used to compare the predicted vs. observed response of a biosensor in the presence of multiple contaminants. For the majority of herbicide interactions, the relationship was not additive but primarily antagonistic and sometimes synergistic. These biosensors provide a sensitive test and are able to screen a large volume and wide range of samples with relative rapidity and ease of interpretation. In this study biosensor technology has been successfully applied to interpret the interactive effects of herbicides in freshwater environments.