Eugenia Valsami-Jones

The ecotoxicology of nanoparticles and nanomaterials: current status, knowledge gaps, challenges, and future needs.

This paper introduces a special issue on the ecotoxicology and environmental chemistry of nanoparticles (NPs), and nanomaterials (NMs), in the journal Ecotoxicology. There are many types of NMs and the scientific community is making observations on NP ecotoxicity to inform the wider debate about the risks and benefits of these materials. Natural NPs have existed in the environment since the beginning of Earth’s history, and natural sources can be found in volcanic dust, most natural waters, soils and sediments. Natural NPs are generated by a wide variety of geological and biological processes, and while there is evidence that some natural NPs can be toxic, organisms have also evolved in an environment containing natural NPs. There are concerns that natural nano-scale process could be influenced by the presence of pollution. Manufactured NPs show some complex colloid and aggregation chemistry, which is likely to be affected by particle shape, size, surface area and surface charge, as well as the adsorption properties of the material. Abiotic factors such as pH, ionic strength, water hardness and the presence of organic matter will alter aggregation chemistry; and are expected to influence toxicity. The physico-chemistry is essential to understanding of the fate and behaviour of NPs in the environment, as well as uptake and distribution within organisms, and the interactions of NPs with other pollutants. Data on biological effects show that NPs can be toxic to bacteria, algae, invertebrates and fish species, as well as mammals. However, much of the ecotoxicological data is limited to species used in regulatory testing and freshwater organism. Data on bacteria, terrestrial species, marine species and higher plants is particularly lacking. Detailed investigations of absorption, distribution, metabolism and excretion (ADME) remain to be performed on species from the major phyla, although there are some data on fish. The environmental risk assessment of NMs could be performed using the existing tiered approach and regulatory framework, but with modifications to methodology including chemical characterisation of the materials being used. There are many challenges ahead, and controversies (e.g., reference substances for ecotoxicology), but knowledge transfer from mammalian toxicology, colloid chemistry, as well as material and geological sciences, will enable ecotoxicology studies to move forward in this new multi-disciplinary field.

Phosphorus Recovery from Wastewater by Struvite Crystallization: A Review

The present review provides an understanding of principles of struvite crystallization and examines the techniques and processes experimented to date by researchers at laboratory, pilot, and full-scale to maximize phosphorus removal and reuse as struvite from wastewater effluents. Struvite is mainly known as a scale deposit causing concerns to wastewater companies. Indeed, struvite naturally occurs under the specific condition of pH and mixing energy in specific areas of wastewater treatment plants (e.g., pipes, heat exchangers) when concentrations of magnesium, phosphate, and ammonium approach an equimolar ratio 1:1:1. However, thanks to struvite composition and its fertilizing properties, the control of its precipitation could contribute to the reduction of phosphorus levels in effluents while simultaneously generate a valuable by-product. A number of processes such as stirred tank reactors and air-agitated and -fluidized bed reactors have been investigated as possible configurations for struvite recovery. Fluidized bed reactors emerged as one of the promising solutions for removing and recovering phosphorus as struvite. Phosphorus removal can easily reach 70% or more, although the technique still needs improvement with regard to controlling struvite production quality and quantity to become broadly established as a standard treatment for wastewater companies.

Lack of OH in nanocrystalline apatite as a function of degree of atomic order: implications for bone and biomaterials

Using laser Raman microprobe spectroscopy, we have characterized the degree of hydroxylation and the state of atomic order of several natural and synthetic calcium phosphate phases, including apatite of biological (human bone, heated human bone, mouse bone, human and boar dentin, and human and boar enamel), geological, and synthetic origin. Common belief holds that all the studied phases are hydroxylapatite, i.e., an OH-containing mineral with the composition Ca10(PO4)6(OH)2. We observe, however, that OH-incorporation into the apatite crystal lattice is reduced for nanocrystalline samples. Among the biological samples, no OH-band was detected in the Raman spectrum of bone (the most nanocrystalline biological apatite), whereas a weak OH-band occurs in dentin and a strong OH-band in tooth enamel. We agree with others, who used NMR, IR spectroscopy, and inelastic neutron scattering, that-contrary to the general medical nomenclature-bone apatite is not hydroxylated and therefore not hydroxylapatite. Crystallographically, this observation is unexpected; it therefore remains unclear what atom(s) occupy the OH-site and how charge balance is maintained within the crystal. For non-bone apatites that do show an OH-band in their Raman spectra, there is a strong correlation between the concentration of hydroxyl groups (based on the ratio of the areas of the 3572 deltacm(-1) OH-peak to the 960 deltacm(-1) P-O phosphate peak) and the crystallographic degree of atomic order (based on the relative width of the 960 deltacm(-1) P-O phosphate peak) of the samples. We hypothesize that the body biochemically imposes a specific state of atomic order and crystallinity (and, thus, concentration of hydroxyl) on its different apatite precipitates (bone, dentin, enamel) in order to enhance their ability to carry out tissue-specific functions.

The complexity of nanoparticle dissolution and its importance in nanotoxicological studies.

Dissolution of nanoparticles (NPs) is an important property that alters their abundance and is often a critical step in determining safety of nanoparticles. The dissolution status of the NPs in exposure media (i.e. whether they remain in particulate form or dissolve - and to what extent), strongly affects the uptake pathway, toxicity mechanisms and the environmental compartment in which NPs will have the highest potential impact. A review of available dissolution data on NPs demonstrates there is a range of potential outcomes depending on the NPs and the exposure media. For example two nominally identical nanoparticles, in terms of size and composition, could have totally different dissolution behaviours, subject to different surface modifications. Therefore, it is imperative that toxicological studies are conducted in conjunction with dissolution of NPs to establish the true biological effect of NPs and hence, assist in their regulation.

The dissolution of apatite in the presence of aqueous metal cations at pH 2–7

Apatite dissolution was studied at 25°C in a series of batch experiments carried out within the pH range of 2–7 with or without the presence of aqueous Pb2+ or Cd2+. The synthetic, microcrystalline hydroxylapatite used in the majority of the experiments was found to have a significantly higher solubility than natural fluorapatite, but a lower dissolution rate. The dissolution rates of both phases increased with decreasing pH. When Pb2+ was present in solution in contact with synthetic hydroxylapatite its concentration decreased over a time interval ranging from several days to several weeks, to a steady state minimum. The rate of Pb2+ loss from solution was sensitive to acidity, and progressed faster at lower pH, but maximum loss was independent of pH. Calcium release to solution matched aqueous lead loss on a mole for mole basis. By the end of each experiment mass calculations suggest that all apatite had been consumed regardless of reaction rate and pH. The solid residue was newly crystallised Pb–hydroxylapatite. This reaction was also observed in situ using Atomic Force Microscopy (AFM) and was found to take place epitaxially onto apatite surfaces. The concentration of aqueous Cd2+ in solution was also reduced in the presence of hydroxylapatite. Cadmium losses were, however, substantially lower. Unlike Pb2+, the maximum amount of Cd2+ lost from solution was a function of pH, and was higher as solution composition approached neutral pH. Cadmium was present in the solid residue at the end of these experiments, probably as a Ca–Cd phosphate solid solution. This work suggests that the interaction between apatite and metals in solution is controlled by apatite dissolution and results in the precipitation of new metal phosphates. The new phosphates nucleate heterogeneously onto the hydroxylapatite surfaces, which acts as a catalyst for the reaction.

Bone and Tooth Mineralization: Why Apatite?

Through evolution, vertebrates have “chosen” the calcium phosphate mineral apatite to mineralize their teeth and bones. This article describes the key characteristics of apatite in biological mineralization and explores how the apatite structure allows biology to control mineral composition and functionality. Through the synthesis and testing of calcium phosphates for biomaterials applications, we have gained further understanding of how sensitive the chemical and physical properties of apatite are to its growth conditions.

Arsenic Pollution Sources

Arsenic is a widely dispersed element in the Earths crust and exists at an average concentration of approximately 5 mg/kg. There are many possible routes of human exposure to arsenic from both natural and anthropogenic sources. Arsenic occurs as a constituent in more than 200 minerals, although it primarily exists as arsenopyrite and as a constituent in several other sulfide minerals. The introduction of arsenic into drinking water can occur as a result of its natural geological presence in local bedrock. Arsenic-containing bedrock formations of this sort are known in Bangladesh, West Bengal (India), and regions of China, and many cases of endemic contamination by arsenic with serious consequences to human health are known from these areas. Significant natural contamination of surface waters and soil can arise when arsenic-rich geothermal fluids come into contact with surface waters. When humans are implicated in causing or exacerbating arsenic pollution, the cause can almost always be traced to mining or mining-related activities. Arsenic exists in many oxidation states, with arsenic (III) and (V) being the most common forms. Similar to many metalloids, the prevalence of particular species of arsenic depends greatly on the pH and redox conditions of the matrix in which it exists. Speciation is also important in determining the toxicity of arsenic. Arsenic minerals exist in the environment principally as sulfides, oxides, and phosphates. In igneous rocks, only those of volcanic origin are implicated in high aqueous arsenic concentrations. Sedimentary rocks tend not to bear high arsenic loads, and common matrices such as sands and sandstones contain lower concentrations owing to the dominance of quartz and feldspars. Groundwater contamination by arsenic arises from sources of arsenopyrite, base metal sulfides, realgar and orpiment, arsenic-rich pyrite, and iron oxyhydroxide. Mechanisms by which arsenic is released from minerals are varied and are accounted for by many (bio)geochemical processes: oxidation of arsenic-bearing sulfides, desorption from oxides and hydroxides, reductive dissolution, evaporative concentration, leaching from sulfides by carbonate, and microbial mobilization. Arsenic enrichment also takes place in geothermally active areas; surface waters are more susceptible than groundwater to contamination in the vicinity of such geothermal systems, and evidence suggests that increased use of geothermal power may elevate risks of arsenic exposure in affected areas. Past and current mining activities continue to provide sources of environmental contamination by arsenic. Because gold- and arsenic-bearing minerals coexist, there is a hazard of mobilizing arsenic during gold mining activities. The Ashanti region of central Ghana currently faces this as a real risk. Historical arsenic contamination exists in Cornwall, UK; an example of a recent arsenic pollution event is that of Ron Phibun town in southern Thailand, where arsenic-related human health effects have been reported. Other important sources of arsenic exposure include coal burning in Slovakia, Turkey, and the Guizhou Province of China; use of arsenic as pesticides in Australia, New Zealand, and the US; and consumption of contaminated foodstuffs (China) and exposure to wood preserving arsenicals (Europe and North America).

Silver Bioaccumulation Dynamics in a Freshwater Invertebrate after Aqueous and Dietary Exposures to Nanosized and Ionic Ag

We compared silver (Ag) bioavailability and toxicity to a freshwater gastropod after exposure to ionic silver (Ag(+)) and to Ag nanoparticles (Ag NPs) capped with citrate or with humic acid. Silver form, exposure route, and capping agent influence Ag bioaccumulation dynamics in Lymnaea stagnalis. Snails efficiently accumulated Ag from all forms after either aqueous or dietary exposure. For both exposure routes, uptake rates were faster for Ag(+) than for Ag NPs. Snails efficiently assimilated Ag from Ag NPs mixed with diatoms (assimilation efficiency (AE) ranged from 49 to 58%) and from diatoms pre-exposed to Ag(+) (AE of 73%). In the diet, Ag NPs damaged digestion. Snails ate less and inefficiently processed the ingested food, which adversely impacted their growth. Loss rates of Ag were faster after waterborne exposure to Ag NPs than after exposure to dissolved Ag(+). Once Ag was taken up from diet, whether from Ag(+) or Ag NPs, Ag was lost extremely slowly. Large Ag body concentrations are thus expected in L. stagnalis after dietborne exposures, especially to citrate-capped Ag NPs. Ingestion of Ag associated with particulate materials appears as the most important vector of uptake. Nanosilver exposure from food might trigger important environmental risks.

Cellular Internalization of Silver Nanoparticles in Gut Epithelia of the Estuarine Polychaete Nereis diversicolor

Silver nanoparticles (AgNPs) are widely used which may result in environmental impacts, notably within aquatic ecosystems. As estuarine sediments are sinks for numerous pollutants, but also habitat and food for deposit feeders such as Nereis diversicolor, ingested sediments must be investigated as an important route of uptake for NPs. N. diversicolor were fed sediment spiked with either citrate capped AgNPs (30 ± 5 nm) or aqueous Ag for 10 days. Postexposure AgNPs were observed in the lumen of exposed animals, and three lines of evidence indicated direct internalization of AgNPs into the gut epithelium. With TEM, electron-dense particles resembling AgNPs were observed associated with the apical plasma membrane, in endocytotic pits and in endosomes. Energy dispersive X-ray analysis (EDX) confirmed the presence of Ag in these particles, which were absent in controls. Subcellular fractionation revealed that Ag accumulated from AgNPs was predominantly associated with inorganic granules, organelles, and the heat denatured proteins; whereas dissolved Ag was localized to the metallothionein fraction. Collectively, these results indicate separate routes of cellular internalization and differing in vivo fates of Ag delivered in dissolved and NP form. For AgNPs an endocytotic pathway appears to be a key route of cellular uptake.

A mesocosm study of fate and effects of CuO nanoparticles on endobenthic species (Scrobicularia plana, Hediste diversicolor).

The fate and effects of CuO nanoparticles (CuO NPs) were examined in endobenthic species (Scrobicularia plana , Hediste diversicolor), under environmentally realistic conditions in outdoor mesocosms (exposure to Cu at 10 μg L(-1) in particulate (CuO NPs) or soluble salt (CuNO(3)) forms) for 21 days. Labile Cu was determined in water and sediment by using diffusive gradient in thin films. No labile Cu being detected from CuO NPs; the observed effects in invertebrates exposed to CuO NPs were mainly attributed to the toxicity of nanoparticulate rather than dissolved Cu toxicity. Bioaccumulation of CuO NPs was observed in both species. Biomarkers were examined at different levels of biological organization: biochemical markers of defense and damage, biomarkers of genotoxicity (comet assay), and behavioral biomarkers (feeding and burrowing). Behavioral biomarkers, antioxidant defenses (catalase, glutathion S-transferase, metallothionein), and genotoxicity are the most sensitive tools to highlight the effect of soluble or nanoparticulate metal forms. Concerning other biomarkers of defense (superoxide dismutase, lactate dehydrogenase, laccase) and damage (thiobarbituric acid reactive substances, acetylcholinesterase, acid phosphatase), no significant effects were detected. This experiment shows the suitability of mesocosms for studying the environmental effects of nanoparticles.