Modelling the Release, Transport and Fate of Engineered Nanoparticles in the Aquatic Environment - A Review.

Engineered nanoparticles, that is, particles of up to 100 nm in at least one dimension, are used in many consumer products. Their release into the environment as a consequence of their production and use has raised concern about the possible consequences. While they are made of ordinary substances, their size gives them properties that are not manifest in larger particles. It is precisely these properties that make them useful. For instance titanium dioxide nanoparticles are used in transparent sunscreens, because they are large enough to scatter ultraviolet light but too small to scatter visible light.To investigate the occurrence of nanoparticles in the environment we require practical methods to detect their presence and to measure the concentrations as well as adequate modelling techniques. Modelling provides both a complement to the available detection and measurement methods and the means to understand and predict the release, transport and fate of nanoparticles. Many different modelling approaches have been developed, but it is not always clear for what questions regarding nanoparticles in the environment these approaches can be applied. No modelling technique can be used for every possible aspect of the release of nanoparticles into the environment. Hence it is important to understand which technique to apply in what situation. This article provides an overview of the techniques involved with their strengths and weaknesses. Two points need to be stressed here: the modelling of processes like dissolution and the surface activity of nanoparticles, possibly under influence of ultraviolet light, or chemical transformation has so far received relatively little attention. But also the uncertainties surrounding nanoparticles in general-the amount of nanoparticles used in consumer products, what constitutes the appropriate measure of concentration (mass or numbers) and what processes are relevant-should be explicitly considered as part of the modelling.

Dancing with the tides: fluctuations of coastal phytoplankton orchestrated by different oscillatory modes of the tidal cycle.

Population fluctuations are often driven by an interplay between intrinsic population processes and extrinsic environmental forcing. To investigate this interplay, we analyzed fluctuations in coastal phytoplankton concentration in relation to the tidal cycle. Time series of chlorophyll fluorescence, suspended particulate matter (SPM), salinity and temperature were obtained from an automated measuring platform in the southern North Sea, covering 9 years of data at a resolution of 12 to 30 minutes. Wavelet analysis showed that chlorophyll fluctuations were dominated by periodicities of 6 hours 12 min, 12 hours 25 min, 24 hours and 15 days, which correspond to the typical periodicities of tidal current speeds, the semidiurnal tidal cycle, the day-night cycle, and the spring-neap tidal cycle, respectively. During most of the year, chlorophyll and SPM fluctuated in phase with tidal current speed, indicative of alternating periods of sinking and vertical mixing of algal cells and SPM driven by the tidal cycle. Spring blooms slowly built up over several spring-neap tidal cycles, and subsequently expanded in late spring when a strong decline of the SPM concentration during neap tide enabled a temporary "escape" of the chlorophyll concentration from the tidal mixing regime. Our results demonstrate that the tidal cycle is a major determinant of phytoplankton fluctuations at several different time scales. These findings imply that high-resolution monitoring programs are essential to capture the natural variability of phytoplankton in coastal waters.

Assessment of azaarenes and azaarones (oxidized azaarene derivatives) in the Dutch coastal zone of the North Sea.

Azaarones (oxidized derivatives of azaarenes) is a group of newly emerging chemical compounds. Little is known about their occurrence in the aquatic environment. Azaarenes are polycyclic aromatic heterocyclic compounds containing one nitrogen atom in one of the aromatic rings. The (photo) oxidized metabolites of the azaarenes are often more toxic than the parent compound. For the first time the concentration of seven azaarenes and seven primary metabolites have been measured in the surface sediments (fraction<63microm) of the Dutch coastal zone of the North Sea. Samples collected in 2000 and 2001 were analyzed using a newly developed method to determine the contents of azaarenes and azaarones simultaneously in a single GC-MS run. The concentrations of acridine, benz[a]acridine, benz[c]acridine and 5,6-benzoquinoline varied between 10-63, 3.9-25, 3.3-11 and 3.98-10.84ngg(-1), respectively. Concentrations of 7,8-benzoquinoline and phenanthridine were below the limit of detection. 2-Hydroxyquinoline and 5-hydroxyquinoline, probably metabolites of quinoline, were present in relatively high concentrations: 7.4-949 and 11-188ngg(-1). A gradient was observed with highest concentrations of the sum of azaarenes and the sum of the concentration of their metabolites close to the coast and lower concentrations further offshore. The concentrations of azaarenes and their metabolites are in the same order of magnitude as those found to induce phototoxicity to algae. The concentrations of mineral oil and PAHs in the surface sediments of the Dutch coastal zone of the North Sea were, at most locations, above the Dutch chemical targets for environmental protection. Spatial distribution of PAHs and mineral oil were slightly different from those of azaarenes and transformation products. Simultaneous GC-MS for azaarenes and their degradation products is possible but extraction/clean up can be further improved. Azaarenes as well as their primary metabolic products are present in the marine environment. In sediments the cumulative concentrations of transformation products amount to about four times the cumulative concentrations of the azaarenes. In conclusion, azaarenes and their metabolites constitute a new group of emerging polycyclic aromatic compounds which need more attention in the future.

Fate of nonylphenol ethoxylates and their metabolites in two Dutch estuaries: evidence of biodegradation in the field.

The environmental behavior of nonylphenol ethoxylates (A9PEO) and their metabolites was investigated in field studies in the two Dutch estuaries Western Scheldt and the Rhine estuary. Using liquid chromatography-electrospray mass spectrometry (LC-ES-MS) analysis after solid-phase extraction, A9PEO, nonylphenol (NP), and the carboxylated metabolites (A9PEC) were determined in surface water and sediments. Maximum dissolved concentrations of 2.3, 0.9, and 8.1 microg L(-1), respectively, were found. In sediments, maximum concentrations of 242 and 1080 ng g(-1) for A9PEO and NP were observed. In almost half of the sediment samples, concentrations of A9PEC in sediments were below the detection limit. Occasionally relatively high values were observed, with a maximum of 239 ng g(-1). Metabolites of the carboxy alkylphenoxy ethoxy acetic acids (CAPEC) type could not be detected in any of the sediment or water samples. In the Scheldt estuary, dissolved concentration profiles showed nonconservative behaviorfor all detected compound groups. While A9PEO and NP concentrations strongly decreased along the salinity gradient, this decrease was weaker for the A9PEC metabolites. The increasing concentration ratio of A9PEC/A9PEO clearly illustratesthe important role that aerobic biodegradation plays in the estuarine fate of these compounds. It is concluded that the oxidative hydrolytic degradation pathway is the main degradation route in this nonstratified estuary. At high salinities, where concentrations drop to background levels of around 50 ng L(-1), this ratio decreases to about unity. Simple model calculations show that this can be explained if continuous diffuse discharges (e.g. from the intensive shipping in the estuary) are assumed. For the stratified Rhine estuary the water concentration profiles are less pronounced, possibly due to more complicated and turbulent water flows and point sources from the Rotterdam harbors.

Environmental and toxicity effects of perfluoroalkylated substances.

The production, use, environmental fate, occurrence, and toxicity of perfluoroalkylated substances have been reviewed. Although only a limited number of essential physicochemical data are available, thus hampering a complete assessment of the environmental fate of PFAS, it has become clear that PFAS behave differently from other nonpolar organic micropollutants. PFAS are present in environmental media in urbanized areas both with and without fluorochemicals production sites. The presence of PFOS at levels above the limit of detection has been demonstrated in almost all organisms sampled in a global survey as well as in both nonexposed and exposed human populations. The acute and chronic ecotoxicity of PFOS, PFOA, and 8:2 FTOH to aquatic organisms is moderate to low. Acute toxicity to rodents is also low. PFOS concentrations in effluents have been reported that approach indicative target values derived from available aquatic toxicity data. PFOA has been found to be weakly carcinogenic. This review shows the importance of the perfluoroalkylated substances for the environment and the necessity to fill the current gaps in knowledge of their environmental fate and effects.

UV absorbance dependent toxicity of acridine to the marine diatom Phaeodactylum tricornutum.

The present study seeks quantitative measures for photoenhanced toxicity under natural light regimes by comparing the effects of an aromatic compound under natural and laboratory light. To this purpose, the influence of light irradiance and spectral composition on the extent of photoenhanced toxicity of acridine, a three-ringed azaarene, to the marine diatom Phaeodactylum tricornutum was analyzed. Under laboratory light containing ultraviolet radiation (UV), the 72-h EC50 growth value for acridine was 1.55 microM. Under natural light, a 72-h EC50 value for acridine below the lowest test concentration (0.44 microM) was observed. Under both laboratory and natural light, the toxicity of acridine was equally enhanced by total UV (UV-A and UV-B) and UV-A radiation, while in the absence of UV no enhancement of toxicity was observed. Hence, the UV-A region of light was dominant in the photoenhanced toxicity of acridine to P. tricornutum, in accordance with its absorption spectrum in the UV-A region. Therefore, the total amount of UV radiation absorbed by aqueous acridine was calculated for each separate treatment. The amount of UV absorbed by acridine effectively described the effect of acridine on the growth of P. tricornutum in a dose-response-dependent manner. It is concluded that photoenhanced toxicity of aromatic compounds expressed as a function of the actually absorbed UV may circumvent some of the variability between studies using different concentrations of the phototoxic compounds and light sources. The UV quantity absorbed by these compounds allows a comparison with the absorption characteristics of natural waters and, thus, is a key parameter to determine the role of photoenhanced toxicity in water.

Enantiomeric enrichment of chiral pesticides in the environment.

Enantiomer fractions (EFs) of chiral compounds have been used to explain the mechanisms of enantiomer enrichment in air, soil, water, and biota. The EFs were calculated from enantiomeric ratios (ERs) of chiral compounds measured by researchers during the past 10 years. Six compounds were selected from different abiotic and biotic compartments: alpha-hexachlorocyclohexane (alpha-HCH), mecoprop, cis-chlordane (CC), trans-chlordane (TC), heptachlor exo-epoxide (HEPX), and oxychlordane (OXY). The EF was used as a general descriptor for enantiomer enrichment. In environmental compartments the EFs of chiral pesticides deviated from those of the racemic composition (EF = 0.5). The deviations from EF = 0.5 in the different compartments show similar patterns for several compounds, i.e., air < water < soil < biota. In biota the order was lower trophic level < higher trophic level and liver or kidney tissue < brain tissue. Explanations for stereoselective behavior were found in pharmacology and brain research. The enantiomeric enrichments in environmental compartments were visualized in a general scheme applicable to other persistent chiral compounds. The mechanisms of enantiomer enrichment were conceptualized by a hypothetical model of a chiral machine (enzymatic degradation) and a chiral guard (stereospecific efflux). Environmental regulation authorities should treat chiral pesticides as a composition of enantiomers because biotic processes handle enantiomers as separate chemical entities.