Mixtures Of Heavy Metals Research Articles

Evaluating combined toxicity of binary heavy metals to the cyanobacterium Microcystis: A theoretical non-linear combined toxicity assessment method

A theoretical non-linear combined toxicity assessment method is proposed and evaluated using Microcystis aeruginosa as the test organism. The combined toxicity of binary heavy metals was evaluated by comparing the actual inhibitory rates shown from the experiments with the theoretically calculated inhibitory rates. It was identified that the binary mixtures of Cu2++ Cd2+, Cu2++ Cr3+ and Zn2++ Cr3+ had the synergistic effects when the combined concentrations were low, but exhibited the antagonistic effects with the higher combined concentrations. Furthermore, the toxic effect of Pb2+ was not influenced by the addition of Cu2+ when combined concentration was low, but it was enhanced by Cu2+ at the high combined concentration. The binary mixtures of Zn2++ Cd2+, Pb2++ Cr3+, Pb2++ Cd2+, Pb2++ Zn2+, and Cr3++ Cd2+ always presented antagonistic effects, while the synergistic toxicity effect on M. aeruginosa was observed for the binary mixtures of Cu2++ Zn2+ regardless of combined concentration. The proposed assessment method was also validated by the antioxidant enzyme activity, which showed synergistic or antagonistic effects under different binary mixtures of heavy metals.

Toxicity assessment due to prenatal and lactational exposure to lead, cadmium and mercury mixtures

The heavy metals lead (Pb), cadmium (Cd) and mercury (Hg) are common environmental pollutants that can be detected simultaneously in blood, serum, and urine samples from the general human population. However, there is limited information regarding toxicity of low-level exposure to Pb, Cd, and Hg mixtures. Our previous research showed the interaction of these three elements at low concentrations in vitro. In this study, we further evaluate early effects of low dose exposure to Pb, Cd, and Hg mixtures on the brain, heart, liver, kidney, and testicle in rats. Pregnant rats were exposed to various concentrations of heavy metal mixtures (MM) in drinking water, during gestation and lactation, and the impacts on offspring were measured at postnatal day 23. Our results showed that the concentrations of Pb, Cd, and Hg in the blood of rat pups were similar to those in the blood of the general human population. Additionally, the MM concentrations in their blood and brain significantly increased in a dose-dependent manner. MM exposure caused histopathological changes in the brain, liver, kidney and testicle. Statistically significant increases in liver CYP450 and PON1, kidney KIM1, and decrease in testicle SDH were observed. In the brain, significant increases were detected in oxidative stress, intracellular free calcium, and cell apoptosis. Further neurobehavioral testing revealed that MM exposure caused dose-dependent impairments in learning and memory as well as sensory perception. MM exposure also disrupted synapse remodeling, which may be associated with pathways involved in dendritic spine growth, maintenance, and elimination. These results suggested that exposure to Pb, Cd, and Hg mixtures, at human environmental exposure related levels, caused damage to multiple organs as well as impairments in neurobehavioral functions of rats. Our findings emphasize the need to control and regulate potential sources of heavy metal contamination.

Exposure to heavy metal-contaminated sediments disrupts gene expression, lipid profile, and life history traits in the midge Chironomus riparius

Despite the concern about anthropogenic heavy metal accumulation, there remain few multi-level ecotoxicological studies to evaluate their effects in fluvial ecosystems. The toxicity of field-collected sediments exhibiting a gradient of heavy metal contamination (Cd, Pb, and Zn) was assessed in Chironomus riparius. For this purpose, larvae were exposed throughout their entire life cycle to these sediments, and toxic effects were measured at different levels of biological organization, from the molecular (lipidomic analysis and transcriptional profile) to the whole organism response (respiration rate, shape markers, and emergence rate). Alterations in the activity of relevant genes, as well as an increase of storage lipids and decrease in membrane fluidity, were detected in larvae exposed to the most contaminated sediments. Moreover, reduced larval and adult mass, decrease of larval respiration rate, and delayed emergence were observed, along with increased mentum and mandible size in larvae and decreased wing loading in adults. This study points out the deleterious effects of heavy metal exposure at various levels of biological organization and provides some clues regarding the mode of toxic action. This integrative approach provides new insights into the multi-level effects on aquatic insects exposed to heavy metal mixtures in field sediments, providing useful tools for ecological risk assessment in freshwater ecosystems.

Exposure to mixtures of heavy metals and metalloids in the adult population of Andalusia

Exposure to mixtures of heavy metals and metalloids in the adult population of Andalusia

Genotoxic and Apoptotic Effects of Heavy Metal Mixture on Human Aortic Vascular Smooth Muscle Cell Line

Objective: Heavy metals are the most common pollutants with specific gravity greater than 5 g cm-3. Human exposure to heavy metals occurs mostly through the consumption of food and water containing heavy metals. Metals that enter the body via drinking water may cause genotoxicity and various diseases. Therefore, permissible limits of heavy metals in water for human consumption have been determined by laws and regulations. Our study aimed to investigate the effects of a mix of metals (Cu, Zn, Pb and Fe) at permissible limits in drinking water on aortic smooth muscle cells (TG-HA-VSMC) with at molecular level. Material-Method: A metal mix at the permissible concentration for drinking water and 10-fold higher concentration were exposed to human aortic smooth muscle for 24 and 48 hours, and gene expression of antioxidant enzymes, heat-shock proteins and apoptosis pathway were investigated in addition to RAPD-DNA polymorphism. Results: It was determined that heavy metal exposure caused increase in the DNA polymorphism, apoptotic cell ratios and enhanced antioxidant and apoptosis pathway gene expression in cells. Conclusion: In conclusion, the mix consisting of heavy metals at permissible limits in drinking water has been shown to cause oxidative stress, genotoxicity and apoptosis in human aortic smooth muscle cells. Considering that apoptosis in vascular smooth muscle cells plays a role in the pathophysiology of diseases such as arteriosclerosis and hypertension, we believe it would be beneficial to assess these limits through extensive investigations in further studies.

Acinetobacter sp. as the key player in diesel oil degrading community exposed to PAHs and heavy metals

The aim of this study was to verify the hypothesis that a hydrocarbon degrading community isolated from a site heavily polluted with polycyclic aromatic hydrocarbons (PAHs) and heavy metals should exhibit a high activity and biodegradation efficiency, despite decreased biodiversity resulting from the presence of such contaminants. Microbial community isolated from soil collected at an abandoned creosote railway wood-sleepers impregnation plant using diesel oil was used during the studies. Four parallel systems spiked with diesel oil, diesel oil + PAHs, diesel oil + heavy metals and diesel oil + PAHs + heavy metals were analysed in terms of relative abundance and biodiversity of the microbial community (Illumina), biodegradation efficiency (GCMS) and cellular metabolic activity (flow cytometry). Principal Component Analysis and biodiversity parameters indicated that the mixture of PAHs and heavy metals was the dominant factor which resulted in the enrichment of the Gammaproteobacteria class. This was associated with higher degradation of additional PAHs in the presence of heavy metals and an increase of metabolically active sub-populations during flow cytometry analysis. The increased abundance of the Acinetobacter genus in systems with both PAHs and heavy metals implies that it may play a crucial role in soil populations exposed to mixed contaminations.

Impacts of point-source Net Alkaline Mine Drainage (NAMD) on stream macroinvertebrate communities

Over 4000 km of Pennsylvania's flowing waters and attendant ecosystems have been degraded by mine drainage to the exclusion of multiple designated uses. Both Acid Mine Drainage (AMD) and Net Alkaline Mine Drainage (NAMD) may result from coal extraction depending on the underlying geology. Acid Mine Drainage is characterized as an acidic mixture of toxic heavy metals in solution, while NAMD is circumneutral in pH with metals forming oxidized precipitates. The ecological impacts of AMD have been well documented but NAMD-impacted streams have received considerably less attention. We selected 10 low-order tributaries of the Ohio and Youghiogheny rivers in southwestern Pennsylvania impacted by point-source inputs of NAMD for assessment of water quality and benthic macroinvertebrate communities. Levels of pH, total iron (Fe), and sulfate (SO4) were significantly elevated in the impacted stream reaches when compared with upstream reference sites while total alkalinity and specific conductance were equivalent. Macroinvertebrate abundance declined by 92% in the impacted stream reaches, but community structure in terms of taxonomic composition and species richness was similar. Total iron, total sulfate, and specific conductance were significantly linked to macroinvertebrate community impairment. The presence of resident macroinvertebrate communities in the unimpacted reaches suggests that remediation would result in a rapid recolonization and establishment of viable downstream ecosystems.

Nitrate-Utilizing Microorganisms Resistant to Multiple Metals from the Heavily Contaminated Oak Ridge Reservation.

Contamination of environments with nitrate generated by industrial processes and the use of nitrogen-containing fertilizers is a growing problem worldwide. While nitrate can be removed from contaminated areas by microbial denitrification, nitrate frequently occurs with other contaminants, such as heavy metals, that have the potential to impede the process. Here, nitrate-reducing microorganisms were enriched and isolated from both groundwater and sediments at the Oak Ridge Reservation (ORR) using concentrations of nitrate and metals (Al, Mn, Fe, Co, Ni, Cu, Cd, and U) similar to those observed in a contaminated environment at ORR. Seven new metal-resistant, nitrate-reducing strains were characterized, and their distribution across both noncontaminated and contaminated areas at ORR was examined. While the seven strains have various pH ranges for growth, carbon source preferences, and degrees of resistance to individual and combinations of metals, all were able to reduce nitrate at similar rates both in the presence and absence of the mixture of metals found in the contaminated ORR environment. Four strains were identified in groundwater samples at different ORR locations by exact 16S RNA sequence variant analysis, and all four were found in both noncontaminated and contaminated areas. By using environmentally relevant metal concentrations, we successfully isolated multiple organisms from both ORR noncontaminated and contaminated environments that are capable of reducing nitrate in the presence of extreme mixed-metal contamination.IMPORTANCE Nitrate contamination is a global issue that affects groundwater quality. In some cases, cocontamination of groundwater with nitrate and mixtures of heavy metals could decrease microbially mediated nitrate removal, thereby increasing the duration of nitrate contamination. Here, we used metal and nitrate concentrations that are present in a contaminated site at the Oak Ridge Reservation to isolate seven metal-resistant strains. All were able to reduce nitrate in the presence of high concentrations of a mixture of heavy metals. Four of seven strains were located in pristine as well as contaminated sites at the Oak Ridge Reservation. Further study of these nitrate-reducing strains will uncover mechanisms of resistance to multiple metals that will increase our understanding of the effect of nitrate and metal contamination on groundwater microbial communities.

Comparison of biochars derived from different types of feedstock and their potential for heavy metal removal in multiple-metal solutions

Three different types of feedstocks and their biochars were used to remove Cr(III), Cd(II), Cu(II) and Pb(II) ions from a mixture of multiple heavy metals. The effect of the initial concentration of heavy metals in solution has been analysed, and kinetics modelling and a comparison of the adsorption capacity of such materials have been performed to elucidate the possible adsorption mechanisms. The results show that the adsorption capacity is dependent on the type of feedstock and on the pyrolysis conditions. The adsorption capacity of the biomass types is ranked as follows: FO (from sewage sludge)>> LO > ZO (both from agriculture biomass waste)>> CO (from wood biomass waste). Biochars, which are the product of the pyrolysis of feedstocks, clearly improve the adsorption efficiency in the case of those derived from wood and agricultural biomasses. Complexation and cation exchange have been found to be the two main adsorption mechanisms in systems containing multiple heavy metals, with cation exchange being the most significant. The pore structure of biomass/biochar cannot be neglected when investigating the adsorption mechanism of each material. All the disposal biomasses presented here are good alternatives for heavy metal removal from wastewaters.

Lead and cadmium induced cytotoxic and genotoxic effects on HL-60 and Jurkat cell lines

Humans are exposed to a mixture of toxic heavy metals in the environment.Because of the lack of information on the toxicity of their mixtures, in thisstudy, two common heavy metals, lead and cadmium, were introducedindividually and as mixtures in HL-60 and JURKAT cell lines for 24 hours.Our experimental results have shown that these two heavy metals inducedcytotoxic and genotoxic effects in both cell lines. Also, cadmium exhibited ahigher cytotoxic and genotoxic potential than lead. The cytotoxicity data ofsingle metals were used to determine the mixtures interaction profile byusing the effect additivity method. Metal mixtures showed synergistic effectin HL-60 cells and antagonistic effect in JURKAT cells, compared toindividual metals. The combined effects should be considered in the riskassessment of heavy metal co-exposure and potency.

High-throughput assessment of toxic effects of metal mixtures of cadmium(Cd), lead(Pb), and manganese(Mn) in nematode Caenorhabditis elegans

Heavy metals, a class of persistent environmental toxicants, are harmful to human health. Cd and Pb are two of the most common toxic heavy metals that have been linked with cancers and malfunction of the nervous system. Notably, contamination of Mn usually coexisted with Cd and Pb in environmental and occupational settings. Studies regularly examined the toxic effects on individual metals; however, potential health and toxic effects of mixtures containing two or more heavy metals are unknown. Here, we investigated toxic effects of Cd, Pb, Mn, and their binary and ternary mixtures in the nematode Caenorhabdities elegans. The toxic outcomes, including effects on growth, reproduction, and feeding, were measured via high-throughput platform analysis. The transgenic strain BY250 with GFP in dopaminergic neurons was used to explore the neurodegenerative effects induced by single metals or their mixtures. The combination index(CI) for mixtures effect was calculated using isobolograms methods. Following the exposure, we found significant toxic effects in C. elegans. For single metals, the toxicity order for growth, reproduction, and feeding were Pb > Cd > Mn. For mixtures, the mixture of Cd + Mn induced a less than addictive effect in C. elegans, whereas the mixtures of Cd + Pb, Pb + Mn, and Cd + Pb + Mn induced greater-than-additive effects. Both single metals and their mixtures induced abnormality in dopaminergic neurons. These results showed combinative toxic and neurodegenerative effects of heavy metal mixtures, and future studies will focus on characterization of concentration-response patterns and identification of potential molecular mechanisms in C. elegans model.

Joint Toxicity of a Multi-Heavy Metal Mixture and Chemoprevention in Sprague Dawley Rats

Background: China is now facing great challenges in heavy metal contamination in the surface water system as well as farmland soil and aquatic products. Exploring the joint toxicity and bio-accumulation of multi-heavy metals and potential chemoprevention strategies will be important for protecting human health. Methods: Male Sprague Dawley (SD) rats were treated orally with 500mg/kg•bw of eight heavy metal composed mixtures including chromium, manganese, nickel, copper, zinc, cadmium, mercury, and lead once a week for 6 months. At the same time, 200mg/kg•bw of epigallocatechin-3-gallate (EGCG), trisodium citrate dihydrate (TCD) or glutathione (GSH) were administered to evaluate their antagonistic effects against adverse effects or bio-accumulation induced by the heavy-metal mixture. After a Morris water maze test, blood samples were obtained for biochemical analysis, and organs (heart, liver, spleen, lungs, kidneys, brain, testis) were collected for biopsy. Inductively coupled plasma mass spectrometer (ICP-MS) was used to analyze the concentrations of heavy metals in serum, tissues or organs. Findings: Finding indicate that 6 months of exposure to a multi-heavy-metal mixture caused a significant reduction of testicle weight, but a significant increase of lung weight, red cell distribution width, serum total bilirubin, indirect bilirubin, and alkaline phosphatase. Histopathological examinations observed prominent pathological changes in the liver and testicle tissues in animals treated with the heavy-metal mixture. ICP-MS results demonstrated that accumulation characteristics of eight different heavy metals in organs and serum varied dramatically. EGCG, TCD or GSH could attenuate the toxic effects induced by a heavy-metal mixture to a certain degree and reduce the concentrations of some heavy metals in the animal body. Interpretation: In summary, long-term intake of multi-heavy metals under this experimental dosage resulted in accumulation in organs and adverse effects on the blood, reproductive system, and liver function. EGCG, TCD or GSH all showed certain chemoprevention effects against the joint toxicity induced by the heavy-metal mixture, which may be attributed to their ability to help drain metals from animals' bodies or their anti-oxidative properties. Funding: This study was partly supported by the National Nature Science Foundation of China (grant no. 81273111), Scientific Projects of Zhejiang Province (grant no. 2015C33148 and 2015C37117), the Ningbo Scientific Innovation Team for Environmental Hazardous Factor Control and Prevention (grant no. 2016C51001), Zhejiang Key Laboratory of Pathophysiology (201703), and the KC Wong Magna Fund of Ningbo University. Declaration of Interest: The authors declare no conflict of interest. Ethical Approval: All animals were housed in a temperature-controlled animal facility (22±2°C) with a 12-hour light/dark cycle (lights on from 7:00 AM to 7:00 PM). All rats had access to water and fodder ad libitum and received humane care in compliance with the Principles of Approval of the Experimental Animal Ethics Committee of Ningbo University.

Assessment of heavy metal contamination in surface sediments along the Mediterranean coast of Morocco.

In this paper, heavy metal contamination in surface sediments along the Mediterranean coast of Morocco was investigated. Determining pollution degree as well as heavy metal origins were the main objectives of this investigation. For this reason, concentrations of nine heavy metals (Cd, Cu, Cr, Ni, Pb, Zn, Hg, Fe, and Mn) were analyzed at ten stations sampled during three different periods. The obtained concentrations showed significant variation between sampling periods, which was controlled by several environmental and chemical processes. According to contamination indices results using pollution load index (PLI), modified contamination degree (mCd), geoaccumulation index (Igeo), enrichment factor (EF), and potential ecological risk index (RI), sampling stations were classified between uncontaminated and strongly contaminated without detecting any intense heavy metal pollution in surface sediment. Likewise, the EF values were comprised between no enrichment and moderate to severe enrichment. According to sediment quality guidelines, the calculated M-ERM-Q indicated that heavy metal mixtures have between 9 and 49% probability for being toxic. This result revealed lowest to medium-low potential of adverse effects to biota populations. Regarding heavy metal origins, multivariate statistical investigation showed that Cd, Cu, Hg, Pb, and Zn are derived mainly from anthropogenic activities, while Fe, Mn, Cr, and Ni were derived from natural sources. Despite Cd is considered as a typical anthropogenic metal, the very low concentrations obtained in this study support the involvement of natural factor in the enrichment with this metal. Therefore, the surface sediments contamination along the Mediterranean coasts of Morocco is particularly caused by a combination of anthropogenic and natural factors. As a result, the study area can be considered as not significantly enriched by human activities.

Simultaneous removal of mixed contaminants, copper and norfloxacin, from aqueous solution by ZIF-8

Many wastewaters commonly contain complex mixtures of both antibiotics and heavy metals, where the simultaneous removal of these mixed contaminants is still a challenge. In this paper, ZIF-8, a metal-organic framework material, was proposed as a potential absorbent to simultaneously remove norfloxacin and copper from wastewater. Batch adsorption experiments showed that ZIF-8 could simultaneously remove 95.4% of Cu and 80.3% of norfloxacin. ZIF-8 was characterized before and after the removal of the mixed contaminants. X-ray powder diffraction (XRD) showed that ZIF-8 was synthesized successfully and maintained a stable structure after contaminant adsorption. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) both suggested that contaminants were partially adsorbed on the surface of ZIF-8. X-ray photoelectron spectroscopy (XPS) also indicated the presence of both carboxyl and Cu on the ZIF-8 surface confirming that a mixture of contaminants was adsorbed. For both contaminants, adsorption followed pseudo-second-order kinetics and best fit the Freundlich adsorption model with correlation coefficients (R2) of 0.973 and 0.994, for copper and norfloxacin, respectively. Finally, removal mechanisms for copper and norfloxacin by ZIF-8 were proposed. For Cu, the adsorption process on ZIF-8 was mainly due to ion exchange, whereas electrostatic interactions and π-π stacking may be responsible for norfloxacin adsorption. Overall this study demonstrated that ZIF-8 was a promising material for the treatment of wastewater containing mixtures of organic and metallic contaminants.

The dynamics of the pharmaceutical and personal care product interactive capacity under the effect of artificial enrichment of soil with heavy metals and of wastewater reuse

A greenhouse experiment was conducted, using a randomized block design, including twelve heavy metal (Mn, Zn, Cu, Cd, Co, Cr, Ni, Pb) mixture treatments, with each metal participating in the treatment with 0, 2, 4, 6, 8, 10, and 12 mg/kg, respectively. Common beet (Beta vulgaris L.) was chosen as test plant. The plants were irrigated with treated municipal wastewater taken from the Wastewater Treatment Plant of the town of Amaliada, N.W., Peloponnese, Greece. The experiment aimed at studying the interactions between heavy metals and macro-microelements, and pharmaceuticals and personal care products (PPCPs). The basic scope was to shed some light on the potential environmental implications, of these interactions on the soil PPCPs for a more effective monitoring of these emerging contaminants in the plants and soil continuum. It was found that the PPCPs have a very high potential interactive capacity, having interacted with all the studied metals, and metalloids, as well as with plant macro elements (P, and K). The uptake of PPCPs by plants was statistically significantly related with their respective content in the soil. The general inference is that the interactive relations between heavy metals, macro-, microelements, and emerging contaminants, being mainly antagonistic, which contribute to the decrease the uptake of soil PPCPs.

Inter-Specific Differences in the Sensitivity, Accumulation and Antioxidant Capacities of Three Cyprinids Exposed to Heavy Metals Mixture

Inter-Specific Differences in the Sensitivity, Accumulation and Antioxidant Capacities of Three Cyprinids Exposed to Heavy Metals Mixture

Variation in metal tolerance associated with population exposure history in Southern toads (Anaxyrus terrestris)

Human activities have radically shaped the global landscape, affecting the structure and function of ecosystems. Habitat loss is one of the most visible changes to the landscape and a primary driver of species declines; however, anthropogenic environmental contamination also threatens population persistence, but is not as readily observed. Aquatic organisms are especially susceptible to chemical perturbations, which can negatively impact survival and fitness related traits. Some populations have evolved tolerance to chemical stressors, which could mitigate the consequences associated with contamination. Amphibians are experiencing global declines due to multiple stressors and are particularly at risk to aquatic chemical stressors due to their permeable skin and reliance on wetlands for reproduction and larval development. However, amphibians also have substantial plasticity in response to environmental variation. We designed our study to examine whether tolerance to heavy metals is greater in Southern toad (Anaxyrus terrestris) larvae from wetlands with a history of contamination. Considering many of the most common trace elements elicit acute toxicity by disrupting osmotic- and ionic-regulation, we hypothesized that alterations to these aspects of physiology resulting from multigenerational exposure to trace element mixtures would be the most likely routes by which tolerance would evolve. We used copper (Cu) as a proxy for heavy metal exposure because it is a widely distributed aquatic stressor known to cause osmotic stress that can also cause mortality at levels commonly encountered in the environment. We found considerable within and among population variation in Cu tolerance, as measured by time to death. Larvae from populations living in sites contaminated with mixtures of heavy metals associated with coal fly ash were no more tolerant to Cu than those from reference sites. However, larvae from a population inhabiting a constructed wetland complex with high Cu levels were significantly more tolerant; having half the risk of mortality as reference animals. This wetland complex was created < 20 years ago, thus if elevated Cu tolerance in this population is due to selection in the aquatic habitat, such adaptation may occur rapidly (i.e. ∼10 generation). Our results provide evidence that amphibians may be able to evolve tolerance in response to trace element contamination, though such tolerance may be specific to the combination of contaminants present.

Exposure to mixtures of mercury, cadmium, lead, and arsenic alters the disposition of single metals in tissues of Wistar rats

ABSTRACTHumans throughout the world are exposed regularly to mixtures of environmental toxicants. Four of the most common heavy metal toxicants in the environment are mercury (Hg), cadmium (Cd), lead (Pb), and arsenic (As). Numerous studies have assessed the effects and disposition of individual metals in organ systems; however, humans are usually exposed to mixtures of toxicants or metals rather than to a single toxicant. Therefore, the purpose of the current study was to test the hypothesis that exposure to a mixture of toxic heavy metals alters the disposition of single metals in target organs. Wistar rats (Rattus norvegicus) were exposed to Hg, Cd, Pb, or As as a single metal or as a mixture of metals. Rats were injected intravenously for three days, following which kidneys, liver, brain, and blood were harvested. Samples were analyzed for content of Hg, Cd, Pb, and As via inductively coupled plasma mass spectrometry. In general, exposure to a mixture of metals reduced accumulation of single metals in target organs. Interestingly, exposure to mixtures of metals with Pb and/or As increased the concentration of these metals specifically in the liver. The findings from this study indicate that exposure to mixtures of toxic heavy metals may alter significantly the distribution and accumulation of these metals in target organs and tissues.

Characterisation of oil sludges from different sources before treatment: High-field nuclear magnetic resonance (NMR) in the determination of oil and water content

Oil sludges are wastes from the oil industry containing complex mixtures of oil hydrocarbons, water, sediments, and heavy metals. These wastes are of main importance for the petroleum industry since it is estimated that more than a billion tons have been stored worldwide. There are several types of oil sludges, but the oil tank bottom sludges are the most studied. Therefore, it is necessary to analyse a variety of oil sludges to establish a detail characterisation, with fast and reliable methods before selecting a suitable treatment. Five sludges were analysed in this study: an oil drilling, oil refinery, oil-water separator, and two waste engine oil sludges. This is a rare report detailing the use of high-field (500 MHz) nuclear magnetic resonance (NMR) to determine oil and water contents in oil sludges, which are more commonly analysed by low-field NMR (below 100 MHz). The proposed NMR procedure was validated by the analysis of oil-water calibration standards (experimental errors < 15%). There was a good agreement among the data obtained from the 1D proton spectra and the Carr-Purcell-Meiboom-Gill (CPMG) T2 decays (percentage differences < 5%). The T2 decays data showed that all sludges had only two components attributed to oil and water, and their relative ratios were determined. The sediment content was determined by the oven-drying method, and the oil hydrocarbon fractions and trace elements were assessed. The oil sludges presented different ranges in the oil, water, sediment and heavy metals contents. The higher presence of C10-C18 aliphatic fractions in the oil from the sludges was an indicator of the potential to be reused as diesel fuel. The sludges had potentially toxic elements (PTEs) values under the limit of the landfilling standards established by the European Union, except for the WSS sludge. Ca and Fe had the highest concentrations in all sludges, which are characteristic of these wastes. The techniques used in this study can be an alternative for a rapid characterisation of the oil sludges, so their most appropriate treatment can be established.

Phytotoxic Effect of Heavy Metal Mixture on Macrophytes

The interaction between inorganic pollutants and higher aquatic plants was studied. Experimental data demonstrated toxic effects from a mixture of heavy metals (Cu, Fe3+, Ni, Fe2+, Zn, Cr6+, Pb, Cd) on Chara fragilis and Callitriche palustris macrophyte species. The experiments were carried out in freshwater microcosms at temperature 12–19°C. Phytotoxicity of the tested mixtures of heavy metals to the macrophytes was revealed. Shoots of C. fragilis and C. palustris plants showed some common signs of phytotoxicity. The new results contribute to the development of water purification phytotechnologies, as well as to elucidation of the range of conditions for applicability of the investigated species in phytoremediation.