Joint effects of heavy metal binary mixtures on seed germination, root and shoot growth, bacterial bioluminescence, and gene mutation

Gene expression and morphological responses of Lolium perenne L. exposed to cadmium (Cd2+) and mercury (Hg2+)

Soil contamination with heavy metals is a major problem worldwide, due to the increasing impact mainly caused by anthropogenic activities. This research evaluated the phytoremediation capacity of, Lolium perenne for heavy metals such as cadmium (Cd²⁺) and mercury (Hg²⁺), and the effects of these metals on morphology, biomass production, and the changes on gene expression. Seeds of L. perenne were exposed to six concentrations of Cd²⁺ and Hg²⁺ in the range of 0 to 25 mg L⁻¹, and two mixtures of Cd²⁺–Hg². The Non-Observed Effect Level (NOEL) was established with dose response curves and the expression of specific genes was evaluated applying a commercially available quantitative reverse transcription (RT-qPCR) assay. There was no significant effect when exposing the seeds to Hg²⁺, for Cd²⁺ the maximum concentration was established in 0.1 mg L⁻¹, and for the two concentrations of mixtures, there was a negative effect. An increase of expression of genes that regulate antioxidant activity and stress was found when the plant was exposed to heavy metals. Given the high tolerance to metals analyzed that was reflected both, the development of the plant and in its molecular response, these results highlight that L. perenne is a plant with phytoremediator potential.

Effects of elevated temperatures and cadmium exposure on stress biomarkers at different biological complexity levels in Eisenia fetida earthworms

Several ecotoxicological studies assessed metal toxicity upon soil biota and other communities but were mainly focused on the study of a single chemical and usually under optimal conditions of temperature. Meanwhile an increasing global warming is leading to new scenarios by combining different stress factors; chemical stress and thermal stress. Presently, this study aims to assess the joint effects produced by cadmium and elevated temperature on earthworms different levels of biological complexity. Eisenia fetida earthworms were maintained at 19 °C and 26 °C and simultaneously exposed to four Cd concentrations (1.25, 2.5, 25 and 125 mg Cd/Kg soil) for 14 (Short term exposure) and 56 days (reproduction test). Endpoints were addressed at different levels of biological complexity: reproductive impairment (cocoons and juvenile productions), Cd tissue accumulation, mortality of adults, weight loss and cytotoxic effects (coelomocyte viability). In the Short term exposure, increase in temperature produced a larger accumulation of Cd. Hence, earthworms exposed to 125 mg Cd/kg soil under heat stress (26 °C) showed a two fold higher Cd accumulation comparing to those at 19 °C. Earthworms exposed to moderate-high concentrations of Cd (2.5-125 mg Cd/kg) and maintained at 26 °C showed severe weight loss and high mortality rates. The neutral red uptake capacity of coelomocytes extruded from earthworms exposed to the highest Cd concentration decreased after 14 d at 19 °C, and more markedly at 26 °C. The reproduction impairment (decreased number of cocoons) was enhanced after exposure to concentrations higher than 2.5 mg Cd/kg at 26 °C, and after exposure to 125 mg Cd/kg at 19 °C. Earthworm reproduction capability is highly vulnerable to the effect of toxicants at elevated temperatures and sublethal concentrations.

Risk assessment of occupational exposure to heavy metal mixtures: a study protocol

Background

Sfax is a very industrialized city located in the southern region of Tunisia where heavy metals (HMs) pollution is now an established matter of fact. The health of its residents mainly those engaged in industrial metals-based activities is under threat. Indeed, such workers are being exposed to a variety of HMs mixtures, and this exposure has cumulative properties. Whereas current HMs exposure assessment is mainly carried out using direct air monitoring approaches, the present study aims to assess health risks associated with chronic occupational exposure to HMs in industry, using a modeling approach that will be validated later on.

Methods

To this end, two questionnaires were used. The first was an identification/descriptive questionnaire aimed at identifying, for each company: the specific activities, materials used, manufactured products and number of employees exposed. The second related to the job-task of the exposed persons, workplace characteristics (dimensions, ventilation, etc.), type of metals and emission configuration in space and time.

Indoor air HMs concentrations were predicted, based on the mathematical models generally used to estimate occupational exposure to volatile substances (such as solvents).

Later on, and in order to validate the adopted model, air monitoring will be carried out, as well as some biological monitoring aimed at assessing HMs excretion in the urine of workers volunteering to participate.

Lastly, an interaction-based hazard index HI_int and a decision support tool will be used to predict the cumulative risk assessment for HMs mixtures.

Discussion

One hundred sixty-one persons working in the 5 participating companies have been identified. Of these, 110 are directly engaged with HMs in the course of the manufacturing process. This model-based prediction of occupational exposure represents an alternative tool that is both time-saving and cost-effective in comparison with direct air monitoring approaches. Following validation of the different models according to job processes, via comparison with direct measurements and exploration of correlations with biological monitoring, these estimates will allow a cumulative risk characterization.

Interactive Effects of Metal Mixtures on Seed Germination and Bioluminescence Activities based on the Theory of Probabilities

The interactive effects of metal mixtures on seed germination (36 combinations) and bacterial bioluminescence (60 combinations) activities were investigated based on the theory of probabilities. Observed effects were compared with expected effects, which were calculated based on single metal activities. Different responses and sensitivities were observed depending on the types and concentrations of mixture metals as well as the organisms tested. In general, an additive mode of action (observed and expected effects are nearly same) was mostly common in the bioluminescence assay, whereas synergistic and additive inhibition modes were mostly observed in seed germination. Therefore, the mixture effects of the different bioassays could not be generalized because they were dependent on the types and concentrations of chemicals and organisms used. The results indicated that mixture, rather than single, effects by various bioassays and wide ranges of concentration combinations may comprise a better strategy for the bioassessment of contaminated environments.

Surface Electrical Potentials of Root Cell Plasma Membranes: Implications for Ion Interactions, Rhizotoxicity, and Uptake

Many crop plants are exposed to heavy metals and other metals that may intoxicate the crop plants themselves or consumers of the plants. The rhizotoxicity of heavy metals is influenced strongly by the root cell plasma membrane (PM) surface’s electrical potential (ψ₀). The usually negative ψ₀ is created by negatively charged constituents of the PM. Cations in the rooting medium are attracted to the PM surface and anions are repelled. Addition of ameliorating cations (e.g., Ca²⁺ and Mg²⁺) to the rooting medium reduces the effectiveness of cationic toxicants (e.g., Cu²⁺ and Pb²⁺) and increases the effectiveness of anionic toxicants (e.g., SeO₄²⁻ and H₂AsO₄⁻). Root growth responses to ions are better correlated with ion activities at PM surfaces ({I^Z}₀) than with activities in the bulk-phase medium ({I^Z}_b) (I^Z denotes an ion with charge Z). Therefore, electrostatic effects play a role in heavy metal toxicity that may exceed the role of site-specific competition between toxicants and ameliorants. Furthermore, ψ₀ controls the transport of ions across the PM by influencing both {I^Z}₀ and the electrical potential difference across the PM from the outer surface to the inner surface (E_m,surf). E_m,surf is a component of the driving force for ion fluxes across the PM and controls ion-channel voltage gating. Incorporation of {I^Z}₀ and E_m,surf into quantitative models for root metal toxicity and uptake improves risk assessments of toxic metals in the environment. These risk assessments will improve further with future research on the application of electrostatic theory to heavy metal phytotoxicity in natural soils and aquatic environments.