Radiocarbon in food: a non-problem of health effects
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Recently it has come to our attention that a paper was published in this journal entitled “recycling greenhouse gas fossil fuel emissions into low radiocarbon food products to reduce human genetic damage” (Williams in Environ Chem Lett 5:197–202, 2007). In this article, it is argued that food grown in a greenhouse is healthier for people, when the greenhouse is fertilised with CO2 prepared from fossil fuels. In this comment, however, we argue that the effect on human health is completely negligible.
KeywordsRadioactivity Food Greenhouse
One of the radioactive isotopes that occur in nature is 14C or Radiocarbon. It has a natural abundance of 14C/12C = 1.2 × 10−12 and a halflife of 5,730 years (e.g., Mook 2006). Radiocarbon is thus present in all forms of natural carbon, including food consumed by humans and animals. Since fossil CO2 is of geological age, all 14C has decayed, and the gas is free of Radiocarbon. Hence, plants that are growing in an environment with an excess of fossil CO2-like greenhouses indeed are depleted in 14C. This is well known in the community of 14C laboratories. For example, the Groningen 14C laboratory has tested tomatoes grown in greenhouses; tomatoes fresh on the market dated to 1,300 years ago. The same is true for the famous Dutch flowers grown in greenhouses; they are less radioactive in 14C than flowers grown outside, and are thus centuries old on the Radiocarbon timescale. This phenomenon is also observed and discussed by Williams (www.radiocarb.com) for soybeans.
Thus, greenhouse grown plants and food sources with a source of fossil fuel–derived CO2 contain less 14C than their naturally grown counterparts. Obviously, this means that a person consuming a consistent diet of 14C depleted food during his or her lifetime is exposed to less radiation from internal 14C sources.
Williams (2007) calculates the number of decays over a human lifespan, which indeed is a large number. Subsequently, the biological impact due to DNA damage is estimated.
This calculation is in itself correct but that does not mean that there is a positive health effect. What is missing from the argument is a calculation of the radiation dose from 14C, natural or depleted, the effect of this dose on human health, and a comparison with other radioactive sources in the environment. Not surprisingly, such a calculation shows that the radiation dose from natural 14C is in itself completely negligible. Even more so for food grown in greenhouses under fossil CO2, depleted in 14C.
The natural radioactivity of 14C is 226 Bq/kgC (e.g., Mook 2006). The halflife is 5,730 years, and 14C is a low-energy beta-emitter (max. 156 keV). The effects of this radioactivity on humans are given by the International Commission on Radiological Protection, ICRP-68 (1995). According to this authority, a “standard person” has a 14C equilibrium activity of 3,500 Bq, and the biological halflife is 40 days. From these numbers, one can calculate that the 14C intake is 2.22 × 104 Bq/year.
The dose rate conversion coefficient for 14C is 5.8 × 10−10 Sv/Bq, for both ingestion and inhalation.
Thus, one derives that the effective dose rate for 14C intake is 13 μ-Sv/year. This is about 1% of the annual dose rate from natural radioactivity, which is generally taken as 1 m-Sv/year. Thus, of all radioactivity exposure due to natural sources, the contribution of 14C can be totally neglected. It is, in effect, a non-problem.
This can also be seen by the following illustrative example calculation.
Vegetables such as soybeans consist mainly of water; for their carbon content, we can assume a general number of 5%. From the natural activity of 226 Bq/kgC and the conversion factor of 5.8 × 10−10 Sv/Bq, one can easily calculate that one has to consume for a year long 400 kg of vegetables per day, in order to get the natural background exposure of 1 m-Sv/year. It seems to us that such a consumption pattern would lead to other more severe negative health effects than caused by 14C radioactivity.
This is calculated for the natural 14C concentration. For greenhouse-depleted 14C, the effect is obviously even less significant. In other words, depleting the 14C content by CO2 in a greenhouse by any practical amount does not contribute in a significant way to more healthy food sources.
We note that in the recent past, the 14C content in nature has been increased by anthropogenic causes, up to a factor of 2. This occured globally by atmospheric nuclear bomb testing during the 1950s and 1960s (e.g., Levin and Hesshaimer 2000) and locally because of the Chernobyl accident in 1986 (e.g., Kovalyukh et al. 1998).
Even then one could still eat 200 kg of vegetables per day. Obviously, this only concerns 14C dose rates. Atmospheric nuclear explosions and the Chernobyl accident also released much more dangerous radioactive isotopes in the environment which are not safe for consumption and which are not discussed here.
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