Nanotechnologies and water: what are the challenges, objectives and means?

Filter membranes with micropores tend to spread to provide drinking water or to desalinate sea water. Nanostructured filter materials are being considered to complement these devices; for example, to filter pesticide and drug residues or to clean up water tables. Is the expected gain in efficiency compared to current treatment solutions sufficient given the cost of the devices? What treatment methods are being used or considered? What are the avenues of research? Does the emission of nanoparticles into water pose a threat to aquatic ecosystems or treatment systems? What, finally, is known and not known about the relationship between nanotechnologies and water? 

As part of the nanoRESP Forum On 5 February 2015, a meeting was held on nanotechnology and water. It was at the Laboratoire national d'essai (Paris 15th) with the following speakers: 

- Auguste Bruchet, chemistry expert, International Centre for Research on Water and the Environment (CIRSEE), Suez Environnement
- Jean-Yves Bottero, Centre de Recherche et d'Enseignement de Géosciences de l'Environnement (CEREGE), Aix-en-Provence
- Catherine Mouneyrac, Institute of Biology and Applied Ecology, Université catholique de l'Ouest (UCO), Angers, Equipe Mer Molécules Santé (MMS), University of Nantes
- José Cambou, Vice-President of ORDIMIP (Observatoire des déchets en MidiPyrénées), National Secretary of the Federation France Nature Environnement (FNE)
- Jean-Luc Laurent (LNE): LNE is contributing to the debate on traceability between the nano and macro worlds. To do this, we need a good understanding of the points of interest of industrialists, scientists and the rest of society. This is the reason for our involvement in the NanoRESP forum.
Animation :
Dorothée Benoit Browaeys, Deputy Editor-in-Chief UP' Magazine - NanoRESP Forum

Ihe original character of this forum must be underlined, whose particular model follows on from experiments carried out over the last ten years, notably the Nanoforum of the CNAM carried out in 2007 to 2009 under the aegis of several ministries. The NanoRESP forum is a stakeholder dialogue with a common concern for vigilance to ensure that innovation is responsible and sustainable. The sessions are built with a pluralist steering committee, and the forum is funded by an alliance of partners: BASF, EDF, SMA BTP, the hydraulic binders association (ATILH) and the measurement and testing laboratory (LNE), which is once again hosting us.
Thanks are due to the networks that relayed the information: LNE's nanometrology club, which will soon be holding an engineering training day on 19 and 20 March, the C'Nano network, the Nanothinking company and the Avicenn association. Cordouan Technologies has also made its presence felt by offering nanotechnological solutions for water treatment, which it is testing in particular in the context of the European Demeau programme.

From the moment we talk about water, we integrate various questions of purification performance but also vigilance regarding the risks that the release of nanoparticles into the environment can pose. This evening's theme therefore raises important issues: the demand for drinking water will increase while at the same time the quality of surface water is declining due to various types of pollution and discharges. A tension will arise between water availability and increasing demand. We will try to address both aspects: treatments, especially those that nanotechnologies would allow, and the new problems that arise with the presence of nanoparticles in water. A recent publication of Brazilian researchers illustrates the complexity of this last point (1).
In the presence of carbon nanotubes, the toxicity of pesticides to a fish, tilapia, is increased fivefold simply because the nanotubes act as transporters of pesticide molecules. Therefore, the effects cannot be treated separately. The "cocktail effects" must be taken on board.

Auguste Bruchet: Suez Environnement's point of view on nanos

Suez Environnement has participated in several projects funded by the French National Research Agency (ANR) on the issue of nanotechnologies, alongside BRGM for example.
The company has two main activities: the treatment of drinking water and wastewater, and the collection and treatment of waste. I will focus here on the
treatment of drinking water.
Rivers such as the Seine - which is used to supply part of the Paris region with drinking water - carry a lot of suspended matter. The first objective of treatment is therefore to remove these materials by a clarification stage; this is carried out by adding a coagulant, iron or aluminium salts to the water, which carries the materials into a decanter. To complete the settling process, the residue is filtered through sand.

In addition, all large plants have an ozone and activated carbon coupling following clarification. Ozone chemically removes odours and micropollutants; the activated carbon adsorbs and physically binds micropollutants that have passed the ozonation stage. The most sophisticated plants, a few dozen in France, add membrane filtration techniques. Suez (via Lyonnaise des eaux) uses ultrafiltration, while Veolia uses nanofiltration. For seawater, reverse osmosis desalination technology (on membrane) with an even smaller spore size is booming.

What happens to the nanoparticles during the clarification stage? An ANR project was conducted on silica (SiO2) nanoparticles. If we compare raw water and treated water, we can see that they sediment in the settling tank because they tend to aggregate. It is also known that a metal such as titanium is well eliminated by the wastewater settling system. 

Ozonation, which oxidizes dissolved organic matter, has no influence on nanoparticles except for C60 (fullerenes). These retain their cage-like structure, but are equipped with oxygen atoms that make the molecule more polar and more soluble in water. Will this facilitate their passage through activated carbon filters, which prefer to retain apolar compounds? It may.
Activated carbon, the next step, is a microporous material that can remove nanoparticles thanks to the size of some pores but allow some to pass through, while retaining apolar molecules such as carbon black.
Suez Environnement has tested modified membrane materials with nanostructured structures, which could be more effective than activated carbon in removing nanoparticles or drug residues. At this stage, the risk of releasing nanos is hindering the development of this approach. The use of nanomanufactured filter materials is being considered in the context of research projects for the removal of refractory compounds or the remediation of polluted groundwater or soil.

Jean-Yves Bottero: Nanotechnology applications for in situ groundwater treatment

I would like to present an example of in situ treatment of polluted groundwater. This treatment has been experimented in the framework of the Nanofrezes project funded by the ANR from 2010 to 2012. Nanofrezes brought together CEREGE (3)the Paul Cézanne University of Aix-Marseille, a Czech subcontracting company, Aquatest, SERPOL, a company specialising in depollution, Hyphen consultants, the'Ineris and the CNRS.

The objective of the project was to develop and experiment with nanoparticles of zero-valent iron (NPFe0, or NZVI) that can be injected into groundwater due to their small size. Zero-valent iron is known to chemically reduce chlorinated solvents such as dichloroethylene (DCE) and trichloroethylene (TCE). These solvents, widely used as cleaners and degreasers, contaminate the groundwater at several thousand sites, mostly industrial, in Europe alone. Zero-valent iron is conventionally used in the form of microscopic or macroscopic particles embedded in permeable barriers.
When NPFe0 oxidizes to iron oxide, it can reduce TCE or DCE to ethane or ethylene. An intermediate transformation, on the other hand, results in dangerous and carcinogenic vinyl chloride.
The first problem to be solved was the transfer of MFNe into the sediment. The physical interactions between nanoparticles and ions in the sediment limit their transport by migration. To reduce these interactions, the surface of the NPFe0 is modified by coating them with polyacrylic acid (polyacrylate), for example.
We tested these coated particles on a source of water contamination at an industrial site in the South of France. These tests showed an increased transfer rate of up to 5 meters around the injection point and an elimination of TCE in 34 days (a longer period than without coating). It is therefore possible to obtain a non-negligible injection radius while maintaining NPFe0 reactivity. Moreover, the selectivity of NPFe0 for chlorinated pollutants is good.
As for the ecotoxicity of these nanoparticles, it does not appear to be a concern. Injection of 0.5 to 1g/L of NPFe0 results in a low risk to aquatic microorganisms. From 0.1 g/L, it is negligible. And finally, the problem does not arise much here since we are on highly contaminated sites. The mobility of nanoparticles is insufficient for them to spread downstream of the injection site. On the other hand, compared to permeable barriers containing zero-valent iron, the injection of NPFe° induces a reduction in bacterial diversity, including sulfate-reducing bacteria, which requires further investigation.
In conclusion, this methodology is developing rather slowly in Europe for cost reasons. The interest is its strong efficiency on the source of contamination over a distance of a few meters.

Discussion on the first two presentations

Dorothée Benoit Browaeys : Is the risk-benefit ratio of these iron particles sufficiently demonstrated?

Jean-Yves Bottero The benefit seems important to me given the high number of sites contaminated by potentially dangerous compounds. (7).

EDITOR'S NOTE : A summary of the risk-benefit ratio of the use of MFNe0 was published in 2014 as part of the European project NanoRem (Nanotechnology for contaminated land Remediation in Europe and beyond) which brings together 28 partners from 13 countries, including BRGM and CNRS in France. It concludes that the positive nature of this report has not yet been clearly demonstrated. The NanoRem project will therefore continue to explore this method.

Caroline Kim-Morange, journalist : When nanoparticles oxidize, do they lose their nanoscale side?

Jean-Yves Bottero Over short time, no, but they evolve into iron oxides while the chlorine is reduced to chlorides.

Dorothée Benoit Browaeys Do you have any points of comparison with conventional methods? Are there other pollutants that can be targeted?

Jean-Yves Bottero Comparison with barriers shows that the nano technique is economically interesting if the source of contamination is treated. The French "market" will probably develop for sites where permeable barriers cannot be used and where the source is to be treated. For the time being, in France, this technique has been used mainly for chlorinated molecules. Additional tests have shown the ability of coated NPFe0 to reduce metals such as chromium VI to chromium III.

Caroline Pétigny, BASF, Copil member: Coming back to the treatment of drinking water, what remains as nanoparticles at the end of the filtration process?

Auguste Bruchet In our analysis, we did not go beyond the clarification stage. Although this step removes 90 % of titanium dioxide (TiO2) or silica (SiO2), it is not known what would happen to the remaining 10 %. It is believed that the activated carbon will allow a number of particles to pass through due to its pore size.

Frédérique Parrot, Sanofi: Have there been any studies on drugs in water? Can we imagine an emergency kit with nanotechnologies dedicated to the filtration of these residues?

Jean-Yves Bottero I don't think so, because the process using iron nanoparticles is not easy to implement.

Auguste Bruchet : To my knowledge, there is no nanotechnology dedicated to drugs in water. At the moment we are already trying to observe how much of the drugs pass into surface and ground water from wastewater with conventional purification processes. As far as is known, what comes out of wastewater treatment plants as doses of medicines is not necessarily dangerous to health, as these are usually doses of less than one nanogram per litre. The water sector is "driven" mainly by regulation. Let's not forget that what led to the development of ozone and activated carbon filters is the European drinking water directive with, in particular, the parameter of 0.1 microgram/L of pesticides. These technologies are also effective in eliminating most drugs. As long as there is no regulation requiring the absence of drugs in drinking water, water distributors will not make the financial effort to set up complementary systems for the few traces of drugs that pass these barriers. Moreover, civil society is probably not prepared to pay this additional cost.

Jean-Yves Bottero : There has been a European programme on the use of nanometric particles on which enzymes are grafted to destroy contaminants in effluents.

Caroline Kim-Morange : I have heard of water treatment companies or industrialists who are positioning themselves on the market for filtration systems incorporating silver as a biocide. Are you aware of the implementation of these systems, and can the nano-silver used end up in the water?

Auguste Bruchet For France, nobody knows the quantity of nano-silver used, according to the Anses declarations (0 kg in 2013). However, this may come from imported products. I have also heard about filter jugs incorporating nano-silver. But I have no further information.

Jean-Yves Bottero In any case, if it passes through water, nano-silver is soluble and transforms into less toxic minerals such as Ag2S. The risk is low.

Dorothée Benoit Browaeys : That's a very smooth transition to the Catherine Mouneyrac subject we are discussing now.

Catherine Mouneyrac: Ecotoxicity of nanomaterials in the aquatic environment

There are various possible pathways for contamination of the aquatic environment by pollutants, including nanomaterials. The main questions to be asked are: what are their transformations in the environment, what is their fate, their behaviour, their concentration in the environment? What is known about their interactions with organisms, their bioavailability and their accumulation in different organs and cells? Are they toxic, and by what mechanisms? Is there a possible transfer into food chains as has been shown for PCBs? Finally, what are their impacts in ecosystems? Each of these questions is far from being elucidated.

The first step is therefore to understand the physicochemical transformations that nanoparticles undergo. Let's take the example of nano-silver. It is transformed by
oxidation and gives compounds that are toxic to some (silver ions), harmless to others (silver sulphide Ag2S). Sulphurization (addition of sulphur to silver to form silver sulphide) is associated with a decrease in toxicity, based on results obtained in one fish species.
The second step is to know the concentrations of the nanoparticles. Unfortunately, monitoring data on these concentrations are not available due to the lack of sufficient analytical techniques in matrices as complex as the aquatic environment. Modelling provides estimates. They are more in the order of micrograms or nanograms per litre than milligrams per litre. However, many toxicity studies use concentrations closer to the milligram per litre, i.e. a thousand times higher.

In fact, for nanoparticles, the dose does not have the same role as for other pollutants. Their physicochemical properties have to be taken into account. In 2008 researchers from Ghent University have shownon a green alga (Pseudokirchneriella subcapitata) in the presence of nanosilica, that what is important for the expression of toxicity is not the concentration mass of the nanoparticles but their surface area. (7).
"When the concentration is expressed in mass, the smallest nanoparticles are more toxic than the largest. However, when the concentration is expressed on the surface, the difference in toxicity disappears. ». To put it plainly, studying toxicity by taking the classic mass concentration parameter is certainly not the right way to go.
What is the exposure of organisms to nanoparticles? Depending on the different aquatic species belonging to different zoological groups and with different life traits (molluscs, crustaceans, fish) that have been tested in recent years, the results vary greatly and cannot really be compared. The life traits are very important: the exposure to nanoparticles is not the same depending on whether the organism lives in the sediment or in the water column.
Before expressing toxicity, it is necessary to know whether nanoparticles accumulate in the body and in which organs. Much work shows that this is the case in
several target tissues. For example, in the scrobicular, a sediment-dwelling bivalve mollusc (Scrobicularia plana), Gold nanoparticles have been found in the nuclei of cells from the digestive gland...with DNA damage. (8).
Once nanoparticles have accumulated, do they induce toxicity? Again, many articles have been published on this point. What emerges is that toxicity is very often associated with oxidative stress, i.e. the formation of oxidative species that can damage the cell, a mechanism that is not specific to nanoparticles. There are also immunotoxic effects, inflammation, genotoxicity (DNA damage), and behavioural changes.

Most of this work has been conducted in the laboratory under controlled conditions, which is very useful in elucidating the mechanisms of toxicity. But what happens in real life? To find out, we use mesocosms, reduced natural ecosystems that allow us to follow natural fluctuations over several years. For example, in an experiment on scrobicularia and a marine worm also living in sediment, toxicities of silver and copper nanoparticles were found to be quite similar between laboratory and field studies using mesocosms. (9).

Where are we at last? We're beginning to understand the cellular mechanisms of toxicity of nanoparticles. But we need techniques that can quantify them in the environment at the low doses at which they occur. We lack studies on the impacts at the population level and over the long term. We need to link information on exposure, changes in physicochemical parameters in the exposure environment, and information on bioaccumulation and potential toxic effects, so that we can run models that can predict long-term effects.

Dorothée Benoit Browaeys : I am a little surprised that you did not go into the explanation of the risks by chemical category of nanomaterials. It is not the same thing to have gold or silver in an organ.

Catherine Mouneyrac : No I didn't categorize, but everyone knows that there are different kinds of nanoparticles. For metallic nanoparticles, the important point is whether they dissolve or not. Do we remain in "nano" issues or not? For silver nanoparticles, dissolution is very high. For dressings, for example, nanoparticles disappear within a week. We are then faced with the problem of silver in metallic form, which is classically toxic. On the other hand, nanoparticles of copper oxide dissolve much less and are therefore considered to be "nano" toxicity. On nanotitanium, there has been a lot of work, particularly on sea urchins, showing toxic effects, but not at the low doses found in the marine environment. In terms of mechanism, however, a specific mechanism of a "nano" effect has not been demonstrated.

Speech by José Cambou

Let's first talk about the manufacture of drinking water: the technical answers are ultrafiltration, nanofiltration, osmosis; but this is only valid for a part of the population, for questions of equipment cost and therefore financial possibilities. This raises questions of equity. As far as waste water is concerned, it is extremely important to act upstream with regard to industrial sources of pollution so that they have their own retention and treatment circuits. The big problem with wastewater is that even if there are filtration methods, there will always be pollutants downstream that go into the aquatic environment, and there is still the problem of sewage sludge, which is commonly used for spreading on agricultural land. Groundwater and rivers can be contaminated in this way. Other inputs to the natural environment are numerous, such as swimming in freshwater or marine waters with sunscreen; there is an increasing amount of material in buildings that ages, erodes and can end up in rainwater or wastewater. As tires wear out, they release nanomaterials that also go into rivers. The end of life of products is also a problem: a lot is thrown away, so we have to talk about leachate. (10) and of course slag, which is used in road underlays, etc., and can be returned to the water cycle. So we have a set of systems that bring nanomaterials into contact with aquatic environments.
There is no simple technical answer to the dispersion of nanoparticles. One could say that these quantities are small. In reality, however, we are seeing a phenomenal increase in the use of "nanotrucmuches" in everyday products. We are on the way to having more and more of them. I insist, because if we stuck to specific uses, the problem of dissemination would not even arise. So there is a risk of pollution of water, a vital element, but also of the food chain in the aquatic environment, with subsequent boomerang effects on humans.
So the environmental and health risk is there. The fundamental question is whether it is socially and ethically acceptable to develop so many nanotechnology-based products when the dangers are not known. The marketing of a product should be determined by its cost-benefit balance. Are futile uses necessary, especially when there is contact with the human body?
It should be noted that the the Environmental ConferenceThe February 4 release of the Nanotechnology Pledge includes two nano-related pledge issues, numbers 67 and 68, which support this view. It states, under objective no. 9 "Improve knowledge and information on the presence of nanomaterials in our environment and propose to Europe to moderate their use": "The French authorities have proposed to the Environment Council of 17 December 2014 that a strategy for the labelling of everyday consumer products containing nanomaterials and the restriction of dangerous products in contact with the skin (particularly with children and pregnant women) be implemented at the European level. A working group will be set up at national level to refine these proposals in the first half of 2015. The conclusions resulting from its work will be forwarded by the French government to the European Commission and the other Member States. » (67)
"A working group will establish a methodological framework (sampling and measurement strategy and method...) to launch a voluntary campaign to measure nanomaterials around a few representative manufacturing sites. » (68)
I was pleasantly surprised to discover this text, all the more so as the restriction of use was one of the points that France Nature Environnement has been advocating since the Grenelle de l'environnement.

Discussion

Jean-Yves Bottero : I would replace the idea of cost-benefit balance with the notion of benefit-risk. There are many applications where there has been no risk assessment but where the benefit is important. For example, isn't it an obvious benefit to make coatings or paints with self-cleaning or depolluting nanomaterials since there is no alternative method?

José Cambou We can see that we need to think on a case-by-case basis by category of nanomaterials or range of uses or manufacturing. It makes no sense to be anti or pro nano. As far as depollution is concerned, the best thing is not to pollute.

Dorothée Benoit Browaeys Can we not go further on the question of organization and prioritization of problems? Some situations are more problematic than others, whereas we have the impression that we are in a bit of a fog, that there is no risk gradient.

Catherine Mouneyrac : As a scientist, I only believe what I see. I don't see any studies that say nanoparticles have an impact on ecosystems. On the other hand, there is evidence that released nanoparticles undergo different transformations that result in various chemicals, each of which can have effects. This is a different situation from that of endocrine disruptors or drug residues.

José Cambou Indeed, for the same type of nanomaterial, you don't have the same effects depending on the particle size. You can never conclude from a single study and we are only at the beginning, and that is why the precautionary principle must be applied as a principle of action, regulation and research.

Catherine Mouneyrac: Where there is a big gap to be bridged is between the multiple physicochemical parameters and toxicity. We're trying to develop models, but it's a long-term process.

Caroline Pétigny Finally, there is a much broader debate about water than just nanotechnology. For example, the balance of benefits and risks concerns any type of product. How can we then make a comparison of the benefit-risk ratio of products, knowing moreover that there is a great deal of subjectivity in the evaluation?

José Cambou For us, nanos are typically an emerging risk: at one time they were confined to research circles and not in the "public square".
Now that they are in the public arena, but this is not accompanied by the means of information so that the population can form an opinion, take ownership of the issue. The way in which regulation is debated and drawn up must involve all stakeholders. That is why we took part in the Nanoforum, why we asked for a public debate, which took place, why an official information site was set up, which did not take place, and why the means of evaluation have increased slightly. At the close of the public debate on nanos, it was acknowledged that out of the public research budget for nanos, only 2 % were devoted to the question of risks.

Dorothée Benoit Browaeys : Precisely, have we made progress in these ways of advancing in the cooperation of actors, knowing that the places of regulation are very little accessible to civil society?

Fernand DoridotICAM researcher, member of Copil NanoRESP: Little progress has been made since the public debate on knowledge sharing, particularly with respect to toxicology studies conducted by industry itself. On the issue of water, I'm still hungry. We are confronted with a context of water that is already heavily polluted by pesticides, etc. We have to deal with this issue. What I take away from the risks or disadvantages associated with the use of nanoparticles is that there are practically none. I have retained an impact on biodiversity And then I have big unknowns about the toxicity to aquatic organisms, but we don't know what this means in terms of the toxicity of PCBs, for example.

Catherine Mouneyrac: Certainly, for PCBs and endocrine disrupters, we have some evidence for possible comparisons in terms of their impacts on populations of organisms. For nanos, this is not yet the case, especially since no specific mechanism of toxicity of nanoparticles has been identified.

Dorothée Benoit Browaeys Are you saying that we should deal with pollutants with known toxic effects first?

José Cambou : I don't think she said that and I hope she didn't! Anticipation is crucial; stop with the "band-aid theory", and try to do some avoidance. If pollutants start to cause problems, we must ask ourselves the question of the uses of products likely to emit these pollutants or their substitutes. We thus know that there are pesticides that must be eliminated and replaced by something else, such as farming methods, knowing that there is never a single good solution, but rather bunches of solutions.

Caroline Kim-Morange Is there not among the physicochemical properties of nanoparticles this capacity to cross cellular barriers, to accumulate in organs where other pollutants can circulate, such as the liver?

Nathalie Thieriet, Anses As has been said, the health and environmental effects of nanomaterials cannot be generalized: a carbon nanotube does not behave at all the same way as a nanotitanium, for example. In order to carry out risk assessment of nanomaterials, a new paradigm, a new approach is needed. The attitude of avoidance as mentioned by José Cambou can be a management method if it is practiced by all levels of society, from those who manufacture nanomaterials to the citizens who use them. The issue of nanomaterials is not just a question of for or against technical innovation, it also involves societal, economic, political and ethical aspects. (12). Concerning the avoidance approach and in order to be able to place a product containing nanomaterials on the market, the industry must consider the appropriate research to be carried out in toxicology and ecotoxicology to assess the risk associated with the use of this product (without necessarily waiting for regulatory indications), and the type of information to be provided to users. But this is an awareness that affects everyone. The marketing of dangerous products already exists, as for example the case of bleach that we all have in our closets. The avoidance system proposed by José Cambou, in a concerted innovation, could prove useful to everyone; it could be built on the innovation stemming from nanomaterials without waiting for the authorities to issue a regulation or for health agencies to come out with an umpteenth assessment of the risks linked to the use of nanomaterials. I would remind you that the REACH dossiers for the registration of conventional chemicals, filled in by manufacturers, must show that they are harmless. However, half of these dossiers have no data. So let's not blame everything on the nanos.

Dorothée Benoit Browaeys How does the evaluation translate into international standardization?

Daniel Bernard, CEA and ISO: What we have found at ISO is that all the published toxicity studies on nanoparticles are virtually null and void because they were done on poorly characterized materials and following non-validated protocols. The ISO has established that at least eight parameters are required to properly characterize a nanomaterial (AFNOR ISO DTR 13014 standard). More than 50 normative documents have been published to date to name and describe nanomaterials. For detection and identification, other documents in preparation will propose protocols that are recognized and validated worldwide.
To get back to toxicity, a position paper was published on 30 January by Australian colleagues who analysed several hundred publications. (13). Beyond that, I agree with what has been said: the great progress is that we now know that we have to categorise, to do so on a case-by-case basis. This is, moreover, what the National Environment Agency (EPA) is doing in the United States with the "Preliminary Manufacture Notification" (PMN) and the idea of "one product, one application". The agency agrees with the manufacturer on a study protocol, and the study is then carried out. Whereas in Europe, with Reach, it's the opposite: you start with the study and only then say whether it is valid or not. On similar products, the Americans have asked for different studies. We will therefore need more and more specialists. Now I agree with José Cambou's remark on the low resources allocated to HSE evaluation: it is difficult to effectively mobilize academic researchers and resources to work on these subjects.

Jean-Pierre Anquetil, Copil member: I represent the OBGTP (General Office for Building and Public Works). We have noticed in the previous sessions that it is difficult to talk about nanomaterials in general. This is why the forum steering committee decided to talk about applications such as water. But here we are talking about water to get back to generalities, and we don't really deal with the subject. For example, what do nanoparticles change to drinking water? What are the thresholds at which they must be eliminated? Those are the kinds of questions I would like to see addressed.

José Cambou You're waiting for answers we don't have.

Jean-Pierre Anquetil I'm not looking for answers, but rather questions that are legitimate to ask, and for the subject of water in particular, at what dosage of nanomaterials water is no longer safe to drink. We could ask the same question for water leaving wastewater treatment plants: at what threshold is it considered to be purified?

Catherine Mouneyrac: You ask the right questions, but it's good that you expect answers, isn't it?

Auguste Bruchet: Why do you focus on drinking water, as do all consumers and the media? We are infinitely more exposed through food if you consider, for example, the quantities of preservatives that contain nanoparticles that we ingest.

(

1) J. Campos-Garcia et al. Ecotoxicological effects of carbofuran and oxidised multiwalled carbon nanotubes on the freshwater fish Nile tilapia: Nanotubes enhance pesticide ecotoxicity, Ecotoxicology and Environmental Safety, Volume 111, January 2015, Pages 131-137 ; see also D S T Martinez et al. Carbon nanotubes enhanced the lead toxicity on the freshwater fish, Journal of Physics: Conference Series 429 (2013)012043. See also link.

(2) Centre for Research and Teaching of Environmental Geosciences, Aix-en-Provence

(7 ) Van Hoecke K et al. Ecotoxicity of silica nanoparticles to the green alga Pseudokirchneriella subcapitata:
importance of surface area. Environ Toxicol Chem. 2008 Sep; 27(9):1948-57.
(8) Joubert Y et al. Subcellular localization of gold nanoparticles in the estuarine bivalve Scrobicularia plana after
exposure through the water. Gold Bulletin March 2013, Volume 46, Issue 1, pp 47-56.
(9) Mouneyrac C et al. Fate and effects of metal-based nanoparticles in two marine invertebrates, the bivalve
mollusc Scrobicularia plana and the annelid polychaete Hediste diversicolor. About Sci Pollut Res Int. 2014
Jul;21(13):7899-912. doi: 10.1007/s11356-014-2745-7.
(10) Products of the percolation of rainwater and runoff through waste.
(12) For more information, read the ANSES report :
https://www.anses.fr/sites/default/files/documents/AP2012sa0273Ra.pdf
(13) Roger Drew & Tarah Hagen. Engineered Nanomaterials: An Update on the Toxicology and Work Health
Hazards, Safe Work Australia, January 2015.

NanoResp Forum - February 2015