Radiocarbon in food: a non-problem of health effects

Abstract

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.

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.