Crop tagging for deforestation enforcement

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On my way to gym today I caught a Living On Earth segment about Greenpeace's efforts to get large soy traders not to buy or distribute soy products produced on cleared rainforest land:
GELLERMAN: But a soybean is a soybean is a soybean. I mean once they're in the bag you don't know where they've come from. How do you enforce that?

ALLEN: Well we don't look at the soybean we look at the farm. So the mapping and the monitoring and the land registration all go together and what we do is we want to have maps to a scale where we can, as soon as we see deforestation happen, we note it. We know who owns that land, we know what has been planted there, we know if it's related to cattle grazer, rice production, soy production, and we then essentially blacklist those farmers so that the traders know that they cannot buy from these farmers even if part of the farmer's land has been used legally to grow soy if they've deforested a new area they will be blacklisted and the traders have agreed to this as part of the moratorium.

This procedure probably will work, but I wonder if there's a technological fix here. The basic idea would be to tag areas of the rain forest with chemical signatures, which would transfer to the soy beans grown in those areas, thus allowing you to determine where a given bean was grown.

The most attractive technique in terms of biocompatibility is to use isotope ratios. For instance, sulfur isotope ratios (S-34/S-32) can be precisely measured and are used as natural environmental tracers. [*]. What we want is an element which is taken up from the soil and is relatively geographically immobile (so that you don't get contamination of neighboring regions). It's possible that there is a set of isotopes that is already characteristic of each region, but more likely we'll need to tag each region so we also want an element with a rare, reasonably long-lived isotope, so that we don't need to spray/dump too much onto the soil in order to bias the isotope ratios in some measurable way. Even better if we have several elements since we can independently vary the ratios to give unique combinations—we may also be able to combine tagging with natural variation if we take measurements. I did a little looking about what elements fit this bill. Some possibilities:

  • Sulfur (S-36 has a .02% fraction)
  • Chlorine (Cl-36 is synthetic and has a 30000 year half-life)
  • Selenium (Se-80 is synthetic with a 30000 year half-life)
  • Potassium (K-40 has a .012% fraction)

Another alternative is to use tagging chemicals. Lots of compounds get taken up by organisms (think DDT, PCBs, etc.), and it shouldn't be that difficult to use compound ratios (perhaps combined with isotope ratios) to produce distinct signatures. The problem here is to find some set of chemistry that everyone agrees is safe to spray over a somewhat inhabited area (again, think DDT, PCBs). We don't really have that problem with isotope tagging as long as we stick to non-radioactive isotopes or isotopes with very long half-lives (remember that there's some baseline radioactivity in the world anyway).


I seem to recall you expressing concern that RSA key-cracking technology, if developed and deployed for laudable purposes, could end up having nefarious applications. Isn't that true in spades for this kind of isotope tagging? Heck, I'm not even a privacy hawk like you, and the thought of the government being able to spray tagging isotopes over an area in order to track who's been there strikes me as just a bit creepy. Is it really worth the risks of having the government deeply invest in this kind of technology, just so that people who care (of whom I'm certainly not one) can tell with a tiny bit more accuracy what part of the world their soybeans have come from?

Hey, I'm just describing how one might do this, not saying one ought to, or lobbying the government to do so. That said, I don't think this would be that useful for tracking "who's been there", since you're not really taking up a lot of trace elements from the soil.

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