Toxicity of a mixture of monoaromatic hydrocarbons (BTX) to a tropical marine microcrustacean

Magnetized vermiculite as a tool for the treatment of produced water generated by oil companies: Effects on aquatic organisms before and after treatment

Produced water (PW) generated by oil companies is a highly impacting waste that contains chemicals such as metals and organic and inorganic compounds. Given its polluting potential, PW requires effective treatment before being discharged into the environment. Conventional treatments have limited efficiency in removing PW toxicity, so alternative approaches must be developed and standardized. In this context, treatment with adsorbent materials like magnetized vermiculite (VMT-mag) is highlighted. This work aimed to evaluate the efficiency of treatment with VMT-mag in reducing PW toxicity to aquatic biota. For this purpose, three aquatic species (the midge Chironomus riparius, the planarian Girardia tigrina, and the crustacean Daphnia magna) were exposed to untreated PW and to PW treated with VMT-mag at laboratory conditions. The assessed endpoints included mortality, growth, emergence, and developmental time of C. riparius; mortality, locomotion, feeding, and head regeneration of G. tigrina; and intrinsic population growth rate (r) and reproductive output of D. magna. The results showed that all the species exposed to raw PW were impaired: C. riparius had delayed development, G. tigrina had reduced locomotor activity and delayed head regeneration, and D. magna had reduced reproduction and delayed intrinsic population growth rate (r). Most of the analyzed parameters showed that treatment with VMT-mag diminished PW toxicity. Therefore, using VMT-mag to treat PW may be the key to reducing the PW effects on aquatic organisms.

Evaluation of joint toxicity of BTEX mixtures using sulfur-oxidizing bacteria

Benzene (B), toluene (T), ethylbenzene (E), and xylenes (X) are petrochemicals vital in various industrial and commercial processing but identified as priority pollutants due to their high toxicity. The objective of this study was to investigate the toxicological nature of BTEX mixtures under controlled laboratory aquatic conditions using sulfur-oxidizing bacteria (SOB). Results from individual BTEX tests demonstrated that the order of toxicity among BTEX was X ≥ E > T > B. Comparisons of dose-effect curves for BTEX suggest that the biochemical mode of action of B in SOB was different from those of T, E, and X. Toxicological interactions of BTEX in mixtures were studied using concentration addition (CA), independent action (IA), and combination index (CI)-isobologram models. The CI model approximated the actual toxicity of BTEX mixtures better than the CA and IA models. In most cases, BTEX induced synergistic interactions in mixtures. However, in some B-containing mixtures, antagonism was observed at low effective levels. The effective level (fa)-CI plots and polygonograms illustrate that synergistic interactions of BTEX became stronger with an increase in effective levels. In addition, ternary and quaternary mixtures were found to provoke stronger synergism than binary mixtures. The present study suggests that the CI-isobologram model is a suitable means to evaluate diverse toxicological interactions of contaminants in mixtures.

Effects of long-term and low-concentration exposures of benzene and formaldehyde on mortality of Drosophila melanogaster

Single-chemical thresholds cannot comprehensively evaluate the risk of chemical mixture exposure in indoor air. Moreover, a large number of researches have focused on short-term and high-concentration co-exposure scenarios related to different species, based on diverse endpoints, which hampers the application and improvement of existing risk evaluation models of chemical mixture exposures. More importantly, current risk evaluation models are not user-friendly for construction practitioners who do not have sufficient toxicological knowledge. Therefore, in this study, an inhalation experiment system and a hazard index (HI) were developed to investigate the risks associated with low-concentration and long-term inhalation exposure scenarios of formaldehyde and benzene, individually and combined, based on Drosophila melanogaster mortality. The results showed that the system exhibited good reproducibility in providing stable exposure concentrations during D. melanogaster life cycle. Furthermore, in a range of experimental concentrations, the interaction between formaldehyde and benzene was additive or synergistic, which was concentration- and ratio-dependent. This study is of great significance in harmonising and providing toxicity data under long-term and low-concentration exposure scenarios, which is beneficial for establishing a new user-friendly risk evaluation model for indoor chemical mixture exposures. It should be noted that the proposed HI value could indicate the hazard degrees of long-term inhalation exposures of formaldehyde and benzene, individually and combined, to D. melanogaster. However, the applicability of this index requires further experiments to evaluate the exposure risks of other volatile organic compounds (VOCs) to D. melanogaster.