Science Interviews


Mon, 14th Dec 2015

Getting to the root of the issue

Professor Chris Collins & Dr John Hammond, University of Reading

Listen Now    Download as mp3 from the show Dishing the Dirt on our Soils

One of the biggest reasons weíre in this sorry state is because of population carrotsgrowth and the resulting intensification of agriculture. But is the poor quality of soil subsequently impacting our food and ultimately therefore, our health? Graihagh Jackson went digging in the dirt with Reading Universityís John HammondÖ

John -   So weíve just dug up some soil here and you can see straight away thereís a huge diversity of ingredients in the soil.  The soil provides a number of things, water, but also some mineral elements; nitrogen, phosphorous, potassium, calcium, magnesium, and sulphur are the six main ones, and then thereís some micro-nutrients that are in there like iron, and copper, and zinc which go into really important functions in the plant

Graihagh - Like what, because I think I need calcium to make my bones stronger, so does the plant need say, phosphorous or nitrogen for?

John - Nitrogenís the biggest one.  The plant needs that in the greatest quantity and that goes into making things like proteins so, if we donít get enough nitrogen in the plant, then the plant canít make chlorophyll and so the plant starts to look yellow.

Graihagh - How does it get from the soil then, into the plant to make the chlorophyll, and make the plant grow ultimately?

John - The plants take up those nutrients from the soil solution, so itís moving water through the soil, up into its roots and out through its leaves, and with that flow of water it can bring with it some of those nutrients.  In particular, nitrogen and sulphur come through that pathway.  Some of the nutrients like phosphorous and potassium, they are harder to move through the water, so they have to move through a diffusion process.  So they move from a high concentration in the soil to a low concentration so that when the nutrients get to the root surface, thereís a number of proteins in the root cell that then transport those nutrients.

Graihagh - And this ultimately enables the plant to grow from a seedling all the way up into an adult crop?

John - Thatís right.

Graihagh - If there are any toxins in the soil, would they be also taken up just like the nitrogen and the phosphorous you were talking about?

John - Yes.  So some heavy metals that we sometimes find in the soils can be taken up through the same process into the plant and, ultimately, into what we would eat.

Graihagh - Thatís not the only way you could ingest heavy metals though.  You could eat the soil itself.  I know what youíre thinking, I donít eat hunks of soil for dinner but, itís actually a lot more common than you think.

Chris - Usually they say about 1% of the weight of a vegetable is the soil attached to it.

Graihagh -   I know, I was quite surprised too Ė 1%.  Thatís a colleague of Johnís at Reading, Chris Collins.  And think about it, how well do you really wash your veggies?  Iím definitely guilty of not scrubbing as well as I should, so thereís probably much more than 1% of my vegetable thatís actually soil...

Chris - Carrots, because there in such intimate contact with the soil are often more contaminated than other crops where the edible portion is above, say for example, a tomato would be much less likely to be contaminated than a carrot.

Graihagh - Although thatís a little hard to stomach, I canít help but think, how bad can it be?  Surely our soils, and certainly the soils that are used to grow food canít be all that polluted Ė right?

Chris - Theyíre very common.  In any urban area you will find detectable levels of lead, from old lead piping, lead in petrol and you will also find elevated levels of the organic pollutants mainly associated with transport but also, for example, a lot of people used to put the ash from their fires into their gardens because they thought it had a nutrient value.  What they didnít realise, is there are some of these organic pollutants associated with those ashes.

Graihagh - What Chris researches is what happens when we eat this polluted soil.  He took me to a lab where theyíre simulating the gut tract from your mouth to your anus.

At one end the polluted soil goes in and is mixed with an acidic solution to recreate the conditions in the stomach.  Next is the small intestines where itís a little bit more alkaline, so the solution in the stomach jar is moved into the intestine jar where something is added to bring that pH up to a more neutral level.  The next bit is the colon and itís where things took a turn for the worse.

Chris - You can get it now.

Graihagh - Oh yes.  I mean itís not great.  Itís getting gradually worse, isnít it? 

What could be so bad?  Well, this is where Chris takes his intestinal samples and mixes them with real human poo.  Yes, you did hear me right.  Hominid excrement Ė and it stinks.


Chris - Itís like being on a farm isnít it?

Graihagh - Yes, but the worst thing is, is I know this is human. Whereas cows, itís slightly more acceptable

Chris - Itís slightly sweeter, isnít it?

Graihagh - Why put yourself through hours of lab time surrounded by the sweet scent of excrement I hear you ask.  Well, these pollutants are syphoned off the soil, left to float around in the gut solution and absorbed into your body.  Whatís known as bio-accessible.

Chris - What weíre looking for is the bio-accessible fraction so, that is the amount of pollutant that is desorbed from the soil into the gut solution.

Graihagh - And how much is bio-accessible from your experiment here?

Chris - 10 to 30% goes into the colon solution.

Graihagh - How much of an affect does your microbiome have on how much of these pollutants you absorb.

Chris - We really don't know because this hasn't been tested. One thing we did test is whether using a polluted soil changed the population composition of the microflora, and actually in the soils we used we didnt find a significant difference between the polluted soils and non polluted soil.

Graihagh -   Does it make a difference to how accesible those pollutants are?

Chris - That might make a superficial difference. They might break them down and turn them into more benign compounds, so they might hydoxilate them for example, which makes them more water soluble and then more likely to be passed out.

Graihagh -   Is there any evidence to suggest that that whole 10 or 30% is then absorbed into the blood?

Chris - Truth is we really donít know.  Thereís been tests in pigs, but thereís a lot of metabolism of organic compounds when theyíre in the body, so itís really difficult to test it.

Graihagh - But I suppose the danger of it being in the bloodstream is that blood goes everywhere.  So equally, if itís not metabolised elsewhere in your liver and excreted through your urine, it could end up in your brain or whatever?

Chris - There is some sort of secondary activity on that, so itís unlikely that the whole amount would be exposed to one particular target organ, if you like, but there is the potential.

Graihagh - Iím not sure how much more of it I can stomach in here.  I can feel myself holding my breath slightly.

Chris - Itís not the most pleasant place to work - but good science.




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