Experimental and predicted acute toxicity of antibacterial compounds and their mixtures using the luminescent bacterium Vibrio fischeri

doi:10.1016/j.chemosphere.2014.01.046

Chemosphere

Volume 108, August 2014, Pages 239-244

https://doi.org/10.1016/j.chemosphere.2014.01.046 Get rights and content

Highlights

•
We tested the effect of triclocarban, triclosan and methyl triclosan on V. fischeri.
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Toxicity was measured both for the three individual chemicals and for their mixture.
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Mixture toxicity was also predicted by concentration addition and independent action.

Abstract

This article investigates the bioluminescence inhibition effects of the antimicrobials triclocarban, triclosan and its metabolite methyl triclosan, using the marine bacterium Vibrio fischeri as the test organism (Microtox©). The concentration response analysis was performed for the three individual substances and for a mixture in which the three compounds were mixed in a ratio of the IC₅₀ of the individual components (equitoxic ratio). Toxicity values (the median inhibitory concentration value, in mg L⁻¹) in the decreasing order of sensitivity were triclosan (0.73) > triclocarban (0.91) > methyl-triclosan (1.76). The comparison of the experimental data with those obtained by using Quantitative Structure–Activity Relationship (QSAR) equations indicated that triclosan and triclocarban act as polar narcotic compounds towards V. fischeri, whereas methyl-triclosan acts as a narcotic (baseline toxicity). The toxicity of the mixture was measured experimentally and predicted by two models (CA: concentration addition; IA: independent action). The results showed that the observed mixture toxicity (IC₅₀ = 0.23 mg L⁻¹) had no significant differences from those predicted by both CA and IA models.

Introduction

The term PCPs (personal care products) refers to several different categories of chemicals widely used in household cleaning, personal hygiene or beautification products, including antibacterials, fragrances, insect repellents, preservatives and UV filters. In general, PCPs are products mainly intended for external use; consequently, unlike pharmaceuticals, they are not subjected to metabolic alterations in human body and can enter the environment basically unaltered through domestic sewers (Ternes et al., 2004). Moreover, there are evidences suggesting that these compounds are only partially eliminated when passing through sewage treatments plants (STP) (Ternes et al., 2004). For this reason PCPs are commonly detected in surface water systems (Peck, 2006) and their occurrence in the aquatic environments has been recognised as one of emerging issues in ecotoxicology (Richardson and Ternes, 2005). Particularly, the extensive use of the antibacterial agents (triclosan: TCS; and triclocarban: TCC) has raised concern about the consequences of their impact on the environment. TCC is added mostly to antimicrobial soaps, whereas the usage of TCS is broader and includes applications in antibacterial mouthwash and toothpaste, as well as in household items, such as plastic cutting boards, sports equipment, textiles, and furniture (Bester, 2003, Sabaliunas et al., 2003, USEPA, 2003). TCS and TCC are among top 10 most commonly detected organic wastewater compounds for frequency and concentration (Kolpin et al., 2002, Halden and Paull, 2005). Several studies highlighted the potential of antibacterial agents to promote adverse effects on aquatic organisms (Schramm et al., 1996, Dietrich and Chou, 2001, Breitholtz et al., 2003, Ishibashi et al., 2004, Gooding et al., 2006, Veldhoen et al., 2006, De Lorenzo and Fleming, 2008, Yang et al., 2008). In addition, other studies indicated that these substances and some of their metabolites (for instance methyl triclosan: TCS–CH₃), can bioaccumulate in aquatic species (Dietrich and Hitzfeld, 2004, Coogan et al., 2007, Coogan and La Point, 2008), and can also be detected in human milk (Rimkus and Wolf, 1996, Adolfsson-Erici et al., 2002) and plasma (Hovander et al., 2002).

In this study, firstly, the effects of TCS, TCS–CH₃ and TCC to the luminescent bacterium Vibrio fischeri were investigated using the Microtox test system. Furthermore, considering that the co-occurrence of PCPs in wastewater treatment plant effluents and in surface water systems is of significant concern (Halden and Paull, 2005), the toxicity to V. fischeri of the equitoxic mixture of the antimicrobial agents (TCC, TCS and its metabolite TCS–CH₃) was also investigated. Finally, the experimental results were compared with those obtained by the application of two predictive models (Concentration Addition: CA and Independent Action: IA) (Loewe and Muischnek, 1926, Bliss, 1939, Greco et al., 1992) often used to calculate the expected mixture toxicity. The first is generally used for the predictive assessment of combination effects and is generally applied to chemicals sharing a common site of primary action. The second (also known as response addition, Bliss independence) is based on the assumption that the mixture components act on different physiological systems of the exposed organism.

Section snippets

Test substances

Triclosan (TCS), CAS [3380–34–5], triclocarban (TCC), CAS [101–20–2] and methyl triclosan (TCS–CH₃), CAS [4640–01–1] were purchased in the highest available purity from Dr. Ehrenstorfer GmbH Laboratories. These chemicals were special-grade reagents and were used without purification. Table 1 reports some physical chemical properties of the tested substances.

The solutions of the tested chemicals were prepared according to the method reported in Vighi et al. (2009). As they exhibit low water

Toxicity test for individual chemicals

Before measuring the joint effects of the mixture, the toxicity of the 3 individual chemicals to V. fischeri was determined. The concentration–response data of the single studied compounds were fitted to Weibull model; the corresponding fitted curves (CRC) are reported in Fig. 1, whereas the IC₅₀ and IC₁₀ values (15 min) are presented in Table 2.

The IC₅₀ of TCS (0.73 mg L⁻¹) obtained in this study is of the same order of magnitude compared to the previously published data (Tatarazako et al., 2004,

Conclusions

The effects of triclocarban, triclosan, its metabolite (methyl triclosan), and their mixture (in the ratio of the IC₅₀ of the individual components) to the luminescent bacterium Vibrio fischeri were determined. The two antibacterial compounds (TCS and TCC) were more toxic than the metabolite. In fact, the comparison of the experimental results with those obtained by two different QSAR equations indicated that the two antibacterial agents act as polar narcotic compounds towards V. fischeri,

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Experimental and predicted acute toxicity of antibacterial compounds and their mixtures using the luminescent bacterium Vibrio fischeri

Highlights

Abstract

Introduction

Section snippets

Test substances

Toxicity test for individual chemicals

Conclusions

Triclosan, a commonly used bactericide found in human milk and in the aquatic environment in Sweden

Chemosphere

Predictability of the toxicity of a mixture of dissimilarly acting chemicals to Vibrio fischeri

Environ. Toxicol. Chem.

Joint algal toxicity of phenylurea herbicides is equally predictable by concentration addition and independent action

Environ. Toxicol. Chem.

Toxicity of binary mixtures of metals and pyrethroid insecticides to Daphnia magna Straus. Implications for multi-substance risks assessment

Aquat. Toxicol.

The preparation and bacteriostatic activity of substituted ureas

J. Am. Chem. Soc.

Triclosan in a sewage treatment process – balances and monitoring data

Water Res.

Triclosan: applications and safety

Am. J. Infect. Control

The toxicity of poisons applied jointly

Ann. Appl. Biol.

Retrospective monitoring of triclosan and methyl-triclosan in fish: results from the German environmental specimen bank

Organohalogen Compd.

A review of personal care products in the aquatic environment: environmental concentrations and toxicity

Chemosphere

Effects of four synthetic musks on the life cycle of the harpacticoid copepod Nitocra spinipes

Aquat. Toxicol.

A review of independent action compared to concentration addition as reference models for mixtures of compounds with different molecular target sites

Environ. Toxicol. Chem.

Biodegradation of triclosan and formation of methyl-triclosan in activated sludge under aerobic conditions

Chemosphere

Snail bioaccumulation of triclocarban, triclosan, and methyl-triclosan in a North Texas, USA, stream affected by wastewater treatment plant runoff

Environ. Toxicol. Chem.

Algal bioaccumulation of triclocarban, triclosan, and methyl-triclosan in a North Texas wastewater treatment plant receiving stream

Chemosphere

Individual and mixture effects of selected pharmaceuticals and personal care products on the marine phytoplankton species Dunaliella tertiolecta

Arch. Environ. Contam. Toxicol.

Ecotoxicology of musks

Bioaccumulation and ecotoxicity of synthetic musks in the aquatic environment

Concepts for the assessment of combined effects of substances: the relationship between concentration addition and independent action

Biometrics

Fate and toxicity of emerging pollutants, their metabolites and transformation products in the aquatic environment

Trends Analyt. Chem.

Predicting the joint algal toxicity of multi-component s-triazine mixtures at low-effect concentrations of individual toxicants

Aquat. Toxicol.

Joint algal toxicity of 16 dissimilarly acting chemicals is predictable by the concept of independent action

Aquat. Toxicol.

Determination of n-octanol/water partition coefficient (Kow) of pesticides: critical review and comparison among methods

Chemosphere

Toxicity of synthetic musks to early life stages of the freshwater mussel Lampsilis cardium

Arch. Environ. Contam. Toxicol.

Consensus on concepts and terminology for combined-action assessment: the Saariselkä agreement

Arch. Complex Environ. Stud.