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Frequently Asked Questions and Answers

What are isotopes?

Isotopes are atoms of the same element, which have the same chemical properties, but different mass because of different number of neutrons in the nucleus. 26 of 92 natural elements in the periodic system have only one natural stable isotope (such as sodium, aluminium, phosphorous or gold – monoisotopic elements), while most of them have two or more (such as hydrogen, sulphur, calcium or iron).

What are stable isotopes?

Stable isotopes are those isotopes, which do not decay and thus emit no ionising radiation into the environment. As stable are considered also those radioactive isotopes, which decay at such a slow rate, that their transformation and emitted radiation cannot be detected with instrumentation presently available.

What are heavy isotopes?

In isotope science, a “heavy isotope” is the stable isotope or stable isotopes of an element, which are heavier than the most abundant isotope. For instance, 18O is considered as heavy oxygen, compared to the most abundant 16O. Heavy isotopes are thus not dangerous – unless, of course, in toxic elements; light cadmium is as toxic as heavy cadmium.

Are there heavy isotopes in food?

Of course. They are natural and therefore they occur everywhere. In every plant or animal tissue, including humans, there are naturally occurring 34S, 15N, 13C, 18O, 2H etc. In total, in the body of an adult man or woman are more than 200 g of heavy isotopes. Since they are omnipresent in every environmental compartment on Earth, we are adapted to them and at natural abundances, they are harmless to plants, animals and the people.

Are heavy isotopes evenly distributed everywhere?

Not exactly. The differences are subtle, but easily measured with modern analytical instruments.

What is isotope composition?

In principle, the simplest way to indicate the isotopic composition of an element is to give the abundance of each isotope in atom %. For instance, about 1 % of all carbon atoms on Earth is 13C or heavy carbon; about 0.36 % of all nitrogen atoms is heavy nitrogen (15N). The differences in abundance of heavy and light isotopes of an element between different reservoirs (such as oxygen in water and plants; or nitrogen in predators and prey) or environmental compartments are usually very small. It would be thus inconvenient to express them in atom % or isotope ratios (such as 18O/16O, 13C/12C). Therefore a relative δ (delta) value is used to express the stable isotope composition of elements, which describes the relative difference between the heavy-to-light isotope ratio in the material of interest and the reference material, expressed in ‰ (per mil). If the δ value of nitrogen (δ15N) of the sample is 0, this doesn’t mean that there is no 15N in it, but that the abundance of the 15N in the sample is exactly the same as in the reference material. If the δ value is positive, then the sample is enriched in 15N compared to the standard, and if it is negative, the sample is depleted in 15N compared to the standard. Reference materials are substances which have the isotope ratio of the element as close as possible to the average isotope ratio of the same element ibn Earth. For example, the reference material for oxygen is ocean water, and reference for nitrogen is air. By definition, the δ value of the reference material is 0 ‰.

What is isotope fractionation?

Briefly, the isotope fractionation is the change in isotope ratios of reaction products compared to the reactants during a chemical reaction (oxidation, dissolution etc.) or phase transition (melting, evaporation etc.).

Why does isotope fractionation occur?

In every chemical or physical reaction, e.g. oxidation or evaporation, the light isotopes react at a slightly higher rate than heavy ones, because the bonds in a molecule or crystal between lighter atoms vibrate with a higher frequency and therefore they split easier than those between heavier atoms. In the products of a chemical reaction are therefore, at least at the beginning, more light isotopes than in the reactants. The consequence is that some substances in nature contain more heavy isotopes (e.g. are enriched in heavy isotopes) than the others, depending on their formation pathway.

A great example of isotope fractionation is photosynthesis: plants preferable absorb light carbon (12C) than the heavy one (13C), therefore they are enriched in 12C (or depleted in 13C) compared to the atmospheric CO2. Isotope fractionation occurs also during phase transitions such as evaporation or condensation, or through exchange of isotopes (for instance between the lake water and air humidity).

What is an (isotopic) fingerprint or signature?

The fingerprint or signature is the combination of δ values of one or more elements and/or elemental ratios and/or other measured parameters that characterise the compound or produce.

All organisms take up elements from the environment, although different elements are taken up at different rates and in different forms. Their elemental and isotopic compositions are in most cases not the same as in the environment (water, soil, food), but nevertheless, they are typical for a region of origin. Plants or animals of the same species from different environments also live in different conditions regarding the temperature, humidity, insolation, soil composition and food sources. Therefore the isotopic compositions of elements in their bodies may slightly differ, however, the difference must not occur in all elements. If we analyse only one element for its isotopic composition, then we simply speak about its isotopic composition – for instance, isotopic composition of nitrogen in mussels cultured at different locations. If we analyse two or more isotopes (beside nitrogen also carbon and maybe even sulphur), then the combination of their δ values (δ13C, δ15N and δ34S) represents the isotopic fingerprint of mussels. In such case, at least one isotope most probably will show some differences and can provide enough information to estimate the origin of mussels. Nevertheless, to estimate the source area of produce, isotopes are not always enough; additionally to the isotopes, the chemical (elemental) composition, e.g. the ratio between different elements, can be used to determine their origin, or even further, the isotopic and elemental ratios in specific compounds of the organisms. Sometimes we even have to analyse the positions of individual isotopes in a specific molecule (for instance the position of deuterium – heavy hydrogen – in the ethanol molecule in wine).

Is water the same all around the world?

No. The H2O molecule undergoes isotopic fractionation at every step of the global water cycle. The isotope composition of both oxygen and hydrogen changes during evaporation of ocean water, condensation of air humidity in clouds, exchange between water and atmospheric water vapour during transport in clouds and during precipitation. Therefore the isotopic composition of precipitation (rain, snow) around the globe varies depending upon several parameters, such as latitude, distance from the ocean, source of water for precipitation, altitude and the temperature. Generally, the δ2H and δ18O values of precipitation decrease with distance from the sea and with altitude, but they also change seasonally: they are lower in astral winter (at low temperature) and higher in astral summer (at higher temperature). Each region of the world has thus a typical range of δ values of precipitation; however, there is no universal formula to calculate the δ2H and δ18O values for each particular spot on Earth.

How do we know the δ2H and δ18O values of precipitation around the globe?

We don’t know the exact δ values for each spot of the globe. The Global Network of Isotopes in Precipitation (GNIP) was initiated by the International Atomic Energy Agency (IAEA) and World Meteorological Organisation (WMO). It is now managed and supported by the IAEA and compiles the data of hundreds of stations all around the world. The stations are mostly managed by the national weather services and voluntarily provide data to the Agency. The database contains data on monthly average temperature, amount and type of precipitation, stable isotope composition (δ2H and δ18O values) and tritium (3H) activity of precipitation.

What is “ERA Chairs”?

ERA Chairs is an FP7 measure aimed to bridge the research and innovation divide in Europe. ERA Chair grants are intended to help develop research excellence in EU Member States, Associated Countries and regions.

What is a nanoparticle?

Nanoparticle (NP) means a minute piece of matter with defined physical boundaries and dimensions lower than 100 nanometers (nm) in one, two or three dimensions; 1 nm = 0.000000001 m = 1.10-9 m.

What is a nanomaterial?

Nanomaterial means a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregated or as agglomerate and where, for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm-100 nm.

What is an engineered nanomaterial?

Engineered nanomaterial means any intentionally manufactured material, containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm to 100 nm.

Where nanoparticles found in food come from?

Nanoparticles (NPs) are added to processed food on purpose by the producers or they derive from contamination from food processing or/and from food contact materials. NPs can also be present in food due to their presence in the environment (soil, air, water), from where they translocate to plants or animals, as remains of use of protective measures (fungicides, pesticides, inorganic antibiotics) or they are formed inside living organisms during their growth.

Why are nanoparticles added to food?

Nanoparticles (NPs) can be added to food for extension of food durability, for taste and nutrition control, for handling control, trade mark protection, facilitation of production and storage, protection against fungi and bacteria, etc. NPs are used in packaging to protect the food from UV light, detect contamination and prevent microbial growth (bacteria, fungi …).

Why are nanoparticles potentially harmful for human health?

The tiny dimensions of nanoparticles (NPs) allow them to pass through the cell walls and, eventually, access the cell nucleus. The potential risks are cell toxicity, genotoxicity, and carcinogenicity. When they enter blood stream, they got translocated and accumulated in specific organs, particularly in those filtrating blood, where their presence can cause harmful effects. Some NPs can penetrate blood-brain barrier with still unknown consequences. They accumulate in food chain and affect environment.

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