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JB



Joined: 08 Jun 2005
Posts: 7748
Location: 91 N
PostPosted: Wed Jul 20, 05 1:07 pm    Post subject: Foraging and pollution  Reply with quote    

If you are collecting wild food how much do you worry about the pollution in its environment?

I collect some wild foods from hedgerows and so on and while it might be exposed to passing traffic the pollution levels are insignifcant, particularly in comparison to the chemicals that get sprayed over non organic produce. At the back of my office there are huge numbers of blackberries but all sitting right over the exhausts of all the cars in the office car park, is that OK? what about fish and river plants that might be getting any amount of run off from farms upstream?

Where would you not forage?

cab



Joined: 01 Nov 2004
Posts: 32429

PostPosted: Wed Jul 20, 05 1:11 pm    Post subject: Reply with quote    

Generally speaking, I don't worry about it too much. I don't pick things from right on roadsides, I don't pick from somewhere obviously contaminated, and I don't pick much straight from river water unless it's clearly clean. But other than that it isn't something I really concern myself with too much.

Have a look here for some useful info:
http://archive.food.gov.uk/maff/archive/food/infsheet/2000/no199/199multi.htm

edit: I would ALWAYS cook finds that have been in freshwater. Always.

JB



Joined: 08 Jun 2005
Posts: 7748
Location: 91 N
PostPosted: Wed Jul 20, 05 1:16 pm    Post subject: Reply with quote    

Useful link, thanks! But so technical and detailed that it begs the question how did you find that so quickly?

cab



Joined: 01 Nov 2004
Posts: 32429

PostPosted: Wed Jul 20, 05 1:19 pm    Post subject: Reply with quote    

JB wrote:
Useful link, thanks! But so technical and detailed that it begs the question how did you find that so quickly?


Because I too am technical and detailed?

Naah, I found it so fast because I've often referred to it in the past. I've been asked the question about pollution and foraging heaven knows how many times.

It's a really, really important question, and it's one that sooner or later most people into foraging will ask, so I like to have the facts to hand to help people come up with an answer.

dougal



Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
PostPosted: Thu Jul 21, 05 1:02 am    Post subject: Reply with quote    

Hmmmm.
The MAFF study is interesting indeed. I'm a little surprised at the weight that can be attached to analysis of just *34* samples from the whole of the UK...

I must say I'd have liked to have seen some justification for their definition of "rural" sample sites as being "more than 20 metres from a road".
Given that definition, and the small sample size, I'm not exactly surprised that there should be no statistically significant differences between lead levels in urban, rural and rural roadside samples...


I'm a bit surprised that Arsenic levels should be quite so high in the mushroom samples.
Although none were *over* the maximum permitted level in commercial foodstuffs, one was just 3% below the threshold.
Since their quality control standard was that repeat measurements had to be within 20%, this seems a bit close to me... And "there was no (statistically) significant difference between arsenic concentrations in urban and rural samples".
Personally, I think it sounds as though there is room for a study of how Arsenic concentration might vary, for example with distance from roads or with local geology.
Agaricus macrosporus showed 4.6 times higher level than the "average" that was used when calculating that the maximum likely exposure from mushrooms was only half the daily maximum (although that was then breached by 8% when other sources of Arsenic were added).

And when calculating the exposure to these pollutants, they seem to reckon that only 2.5% of foragers would ever eat more than 27g (dry weight) of mushrooms in a day. A small packet of dried ceps is 25g. Methinks they underestimate the amount of occasional bingeing! (And therefore the maximum single day exposure will be comfortingly underestimated too.)
And on that basis a 60kg bodyweight consumer of 27g of their average mushrooms would be getting a Cadmium dose of 72% of the FAO/WHO maximum from mushrooms alone!
And given that the Cadmium reported in Agaricus Macrosporus seems to be 12.5 times higher than the average for all mushrooms tested, someone eating a lot of that particular species would appear to be way over the threshold of advisability for Cadmium as well as Arsenic.

Which brings me to another concern with these statistics.
While particular species of mushroom are shown to have differing propensities to take up different metals, is it fair to simply "average" the pollutant concentration across all species?
IMHO, it would be more realistic to "weight" the average, based on the relative abundance of those species in foragers' baskets? (And yes, that will vary through the season.)

"Five of the thirty-four samples of fungi had lead concentrations higher than the legal limit of 1 mg/kg that would apply to commercial samples of fungi." (COT in the Annex)

As the report says "Several samples of wild fungi showed the ability to accumulate some relatively high concentrations of certain elements, especially cadmium, copper, arsenic, mercury, zinc and lead. This is consistent with earlier studies which show that certain fungi can accumulate very high concentrations of metals."
The earlier papers are entitled "Concentrations of mercury, copper, cadmium and lead in fruiting bodies of edible mushrooms in the vicinity of a mercury smelter and a copper smelter" and "Absorption of heavy metals in wild berries and edible mushrooms in an area affected by smelter emissions".


http://archive.food.gov.uk/maff/archive/food/infsheet/1997/no108/108fungi.htm
"A SURVEY OF RADIOCAESIUM CONTAMINATION LEVELS AND ESTIMATIONS OF DIETARY INTAKE OF EDIBLE WILD FUNGI"
Snippets -
"Radiocaesium activity concentrations in the fruit bodies of some species of edible wild macrofungi are higher than in many other foods because fungi are known to accumulate trace elements including radionuclides. In some countries where the collection of wild fungi is traditional and in areas which were affected by the deposition from the Chernobyl accident, the consumption of wild mushrooms could provide a substantial intake of radiocaesium.
As part of the Working Party on Radionuclides in Food's (WPRF) surveillance, a survey was carried out to investigate the levels of radiocaesium in the most frequently eaten wild fungi in England and Wales and estimates made of the dose to consumers."
"In total 394 fungal samples representing 37 different species were collected throughout England and Wales."
"In general, radiocaesium concentrations were 1 to 2 orders of magnitude {that is 10x to 100x} higher in mycorrhizal species (e.g. those found in woodlands like the Boletus) than saprotrophic species (e.g. those in grasslands like the common field mushroom) or parasitic species (e.g. Honey Fungus)."
"Activity concentrations of the most commonly eaten field and horse mushrooms were low, less than 30 bequerel per kilogram (Bq/kg) of caesium dry weight (DW), or less than 2 Bq/kg of caesium fresh weight (FW) although the maximum recorded concentration in any fungi was 4540 Bq/kg of caesium DW from a sample of Brown Birch Bolete from west Cumbria." {Strangely enough, Sellafield is in west Cumbria...}
"Plutonium and radiostrontium activity concentrations were investigated in 5 samples. These samples were selected on the basis that they either had high radiocaesium contents or were from sites within a 3 km radius from the Sellafield reprocessing plant. It was found that activity concentrations of strontium and plutonium were generally low, with the exception of one sample of Shaggy Ink Cap from the grassy saltmarshes on Morecambe Bay which had 2.35 Bq/kg DW of plutonium, contaminated by marine discharges from Sellafield. "
"The essential conclusion from this survey is that radiocaesium levels present in wild fungi in England and Wales are acceptable..."


My personal reading of the MAFF reports is that specific fungi can have dramatically high levels of heavy metal pollutants.
Accordingly, it would seem to make sense not to collect them from anywhere in the vicinity of industrial activity. And there's not much difference in pollutants between the roadside and 20 metres away.
It certainly doesn't look as though its advisable to binge on one species collected from one site - especially A macrosporus, sad because Phillips suggests it can grow beyond 25cm diameter, although it does look *very* like the field mushroom A campestris.
But, yes, if you eat an "average" quantity of mixed "average" mushrooms from all round the country, it looks as though you should be safe enough.
Although the chances of exceeding the recommended limits, by eating too much of a receptive species from a bad site, appear rather higher than I would have expected.
I suppose 34 samples just isn't enough to begin to properly quantify those risks - which I think is what we really want to know!
Oh, and *woodlands* in the Lake District look as though they should be added to the list of dodgy sites...

jema
Downsizer Moderator


Joined: 28 Oct 2004
Posts: 26649
Location: escaped from Swindon
PostPosted: Thu Jul 21, 05 5:37 am    Post subject: Reply with quote    

dougal wrote:
Hmmmm.
The MAFF study is interesting indeed. I'm a little surprised at the weight that can be attached to analysis of just *34* samples from the whole of the UK...


That does sound crap Coincidentally I am just running an analysis based on a daily sample of a little under 50 items. Yesterdays "conclusion" would be the exact opposite of todays! Not that I would be daft enough to jump to a conclusion on a days result at that sample size. Unless you know in advance that there are no unkown random biases in the data, you need samples taken over reasonable periods of time in reasonable quantities. Of course if you know enough about the data to discount there being any odd biases, then you had no need to run the experiment in the first place.

JB



Joined: 08 Jun 2005
Posts: 7748
Location: 91 N
PostPosted: Thu Jul 21, 05 9:03 am    Post subject: Reply with quote    

jema wrote:
dougal wrote:
... I'm a little surprised at the weight that can be attached to analysis of just *34* samples from the whole of the UK...


... Coincidentally I am just running an analysis based on a daily sample of a little under 50 items


In my dim and distant past (well ok not so very distant but possibly dim!) I worked with sample sets this small and smaller (it's a little bit difficult to get a large sample of red giants into the lab at any one time ) and you can get useful results from them but generally only for very well understood processes, to generate hypotheses to be tested in future studies or to disprove an existing hypothesis.

That sample could disprove the hypothesis 'fungi 20m from roads contain no significant heavy metal pollutants' but could not prove the same hypothesis to be true as the 35th sample could significantly alter the results.

cab



Joined: 01 Nov 2004
Posts: 32429

PostPosted: Thu Jul 21, 05 10:30 am    Post subject: Reply with quote    

dougal wrote:
Hmmmm.
The MAFF study is interesting indeed. I'm a little surprised at the weight that can be attached to analysis of just *34* samples from the whole of the UK...


It's one of those things where the process is rather well characterised. Mushrooms and other fungi have been used in many applications for sopping metal ions out of solutions; most often research work has centred on spent Aspergillus or Penicillium myceliu, but also mycelium of Agaricus, Pleurotus and other basidiomycetes. If you want to be picky, I've never seen anyone do this with an Ascomycete, so maybe something like a morel could be different, but as the process by which fungi hold onto heavy metal ions is fairly well understood and based more on cell wall components than anything else, and as the chemistry of cell walls of Ascomycetes and Basidiomycetes ain't that different, in my view that would be overly picky. It doesn't matter whether there are 34 samples or 340 samples from the UK, what matters is that the samples are representative; you need to have enough (six would be nice) from each type of habitat you're most interested in, and this study concentrated on such habitats.

Quote:

I must say I'd have liked to have seen some justification for their definition of "rural" sample sites as being "more than 20 metres from a road".
Given that definition, and the small sample size, I'm not exactly surprised that there should be no statistically significant differences between lead levels in urban, rural and rural roadside samples...



I don't get you. They need to use a definition, so they picked one that at least made some kind of sense. Proximity to a road is a fairly good one, because the specific pollutants they were looking for don't travel a great distance from roads before they get onto the ground, at which time they become bound to something very fast. These metal ions are like that.

Quote:
I'm a bit surprised that Arsenic levels should be quite so high in the mushroom samples.
Although none were *over* the maximum permitted level in commercial foodstuffs, one was just 3% below the threshold.
Since their quality control standard was that repeat measurements had to be within 20%, this seems a bit close to me... And "there was no (statistically) significant difference between arsenic concentrations in urban and rural samples".
Personally, I think it sounds as though there is room for a study of how Arsenic concentration might vary, for example with distance from roads or with local geology.


That would indeed be interesting, but then again having a few samples being close to such limits (which are set well below any practical toxic levels) isn't something I would lose any sleep over.

Quote:
Agaricus macrosporus showed 4.6 times higher level than the "average" that was used when calculating that the maximum likely exposure from mushrooms was only half the daily maximum (although that was then breached by 8% when other sources of Arsenic were added).

And when calculating the exposure to these pollutants, they seem to reckon that only 2.5% of foragers would ever eat more than 27g (dry weight) of mushrooms in a day. A small packet of dried ceps is 25g. Methinks they underestimate the amount of occasional bingeing! (And therefore the maximum single day exposure will be comfortingly underestimated too.)


Again, while that's true, eating an entire 25g packet of dried ceps on your own is pretty massive consumption; I've never got through so much, and I find if I put too much dried Boletus into a dish that it is very overpowering. As for Agaricus macrosporus, it's a fairly damp mushroom that in my experience dehydrates leaving less dry biomass than other Agaricus species, and WAY less than Boletus edulis; to eat more than 27g dry weight of it in a day would be difficult. Well, I'd find it bloody hard.

Put this into perspective; these metal (and metalloid) ions are universal. We know that they are accumulated in quite some quantity by leaf degrading fungi that are edible. We know that spreading manure onto agricultural land has the effect of increasing the concentration of such ions, and we know that both organic and inorganic materials added in agriculture (blod fish and bone, growmore, insecticides and bioinsecticides) all contain them at trace levels, and that the concentration of such ions on land exists in an equilibrium between how many are added, and how many bind to the removable biomss (including crops).

Quote:
And on that basis a 60kg bodyweight consumer of 27g of their average mushrooms would be getting a Cadmium dose of 72% of the FAO/WHO maximum from mushrooms alone!
And given that the Cadmium reported in Agaricus Macrosporus seems to be 12.5 times higher than the average for all mushrooms tested, someone eating a lot of that particular species would appear to be way over the threshold of advisability for Cadmium as well as Arsenic.


I don't see it that way; what I see is a low legal threshold that you'd really have to go to town on A. macrosporus (something that isn't likely), and even then you'd be going over a legal advisable level that is below that which would really trouble a toxicologist. Add to that the fact that this isn't a study that sits alone; The EU has gone into some depth specifically on cadmium if you're interested:

http://www.ktbl.de/english/projects/aromis/smolders.pdf

Quote:

Which brings me to another concern with these statistics.
While particular species of mushroom are shown to have differing propensities to take up different metals, is it fair to simply "average" the pollutant concentration across all species?
IMHO, it would be more realistic to "weight" the average, based on the relative abundance of those species in foragers' baskets? (And yes, that will vary through the season.)


I can see where you're coming from with that, but lets look at the practicalities.

On a good day, wandering around Nottingham University Campuss (hardly a pristine site for wildlife) I used to go home with a bag containing three dozen species. In Thetorf forest, last time I was up there, we picked samples of about a dozen species. I've picked something like 30 species in my local woodland, a scrubby patch by a disused railway line, and there are probably a dozen or more good edible species that I might to expect on a typical housing estate. As a rough guesstimate, I've picked and eaten over 200 species of mushroom.

Would it be practical to measure the levels of all potential contaminants in all potential baskets, and is it even desirable to do so when there's no obvious reason to suppose anyone is at risk? Or is it a better idea to do a trancect from a potential site of contamination?

Quote:
"Five of the thirty-four samples of fungi had lead concentrations higher than the legal limit of 1 mg/kg that would apply to commercial samples of fungi." (COT in the Annex)

As the report says "Several samples of wild fungi showed the ability to accumulate some relatively high concentrations of certain elements, especially cadmium, copper, arsenic, mercury, zinc and lead. This is consistent with earlier studies which show that certain fungi can accumulate very high concentrations of metals."
The earlier papers are entitled "Concentrations of mercury, copper, cadmium and lead in fruiting bodies of edible mushrooms in the vicinity of a mercury smelter and a copper smelter" and "Absorption of heavy metals in wild berries and edible mushrooms in an area affected by smelter emissions".


Yeah, it's mostly the divalents, isn't it. They'll sop up nickel and iron too, I rekon. But again, unless you're eating from really contaminated sites (heck, who's picking near a smelter?) then I'm not too worried by this.

Quote:

http://archive.food.gov.uk/maff/archive/food/infsheet/1997/no108/108fungi.htm
"A SURVEY OF RADIOCAESIUM CONTAMINATION LEVELS AND ESTIMATIONS OF DIETARY INTAKE OF EDIBLE WILD FUNGI"
Snippets -
"Radiocaesium activity concentrations in the fruit bodies of some species of edible wild macrofungi are higher than in many other foods because fungi are known to accumulate trace elements including radionuclides. In some countries where the collection of wild fungi is traditional and in areas which were affected by the deposition from the Chernobyl accident, the consumption of wild mushrooms could provide a substantial intake of radiocaesium.


It was a sad reality that for years following the Chernobyl catastrophe, wild mushrooms across some of Northern England and other places were best considered off limits Whether that's an issue now... Well, I wouldn't pick from right on the backdoor of Sellafield. Back in the mid 90's (95 I think it was) we waved samples under a Geiger counter in Lancaster, and found that they crackled less than chellfish you could buy that were gathered in Morecambe bay; wasn't enough in them to worry me.

Quote:
As part of the Working Party on Radionuclides in Food's (WPRF) surveillance, a survey was carried out to investigate the levels of radiocaesium in the most frequently eaten wild fungi in England and Wales and estimates made of the dose to consumers."
"In total 394 fungal samples representing 37 different species were collected throughout England and Wales."
"In general, radiocaesium concentrations were 1 to 2 orders of magnitude {that is 10x to 100x} higher in mycorrhizal species (e.g. those found in woodlands like the Boletus) than saprotrophic species (e.g. those in grasslands like the common field mushroom) or parasitic species (e.g. Honey Fungus)."


This always surprised me; why do you suppose that is?

Quote:

"Activity concentrations of the most commonly eaten field and horse mushrooms were low, less than 30 bequerel per kilogram (Bq/kg) of caesium dry weight (DW), or less than 2 Bq/kg of caesium fresh weight (FW) although the maximum recorded concentration in any fungi was 4540 Bq/kg of caesium DW from a sample of Brown Birch Bolete from west Cumbria." {Strangely enough, Sellafield is in west Cumbria...}


True enough, but remember that West Cumbria also caught the worst of the rain that dropped crap from Chernobyl on Britain. As you've read from the rest of the report, Sellafield is a realistic culprit for pollution in the salt marshes up there, more so than it is for the above contaminant.

Quote:

"Plutonium and radiostrontium activity concentrations were investigated in 5 samples. These samples were selected on the basis that they either had high radiocaesium contents or were from sites within a 3 km radius from the Sellafield reprocessing plant. It was found that activity concentrations of strontium and plutonium were generally low, with the exception of one sample of Shaggy Ink Cap from the grassy saltmarshes on Morecambe Bay which had 2.35 Bq/kg DW of plutonium, contaminated by marine discharges from Sellafield. "


That's the ticket; that's one you really CAN blame Sellafield for

Quote:

"The essential conclusion from this survey is that radiocaesium levels present in wild fungi in England and Wales are acceptable..."


My personal reading of the MAFF reports is that specific fungi can have dramatically high levels of heavy metal pollutants.
Accordingly, it would seem to make sense not to collect them from anywhere in the vicinity of industrial activity. And there's not much difference in pollutants between the roadside and 20 metres away.
It certainly doesn't look as though its advisable to binge on one species collected from one site - especially A macrosporus, sad because Phillips suggests it can grow beyond 25cm diameter, although it does look *very* like the field mushroom A campestris.
But, yes, if you eat an "average" quantity of mixed "average" mushrooms from all round the country, it looks as though you should be safe enough.


I agree with a lot of that; I'll add, though, that you'll most likely make yourself more ill worrying about it than you would by getting an overdose of nasty metal ions in mushrooms. Oh, and if you find yourself some A. macrosporus, they really are a treat Better than a field mushroom, as good as a horse mushroom, not as good as a prince. Not quite. Although my taste there varies with my mood.

To say that you ought to avoid anywhere in the viscinity of industrial activity is harsh, I think, but again, if eating mushrooms from anywhere close to industry at all will worry you, don't do it. More left for me (yaay!)

Quote:

Although the chances of exceeding the recommended limits, by eating too much of a receptive species from a bad site, appear rather higher than I would have expected.
I suppose 34 samples just isn't enough to begin to properly quantify those risks - which I think is what we really want to know!
Oh, and *woodlands* in the Lake District look as though they should be added to the list of dodgy sites...


Depends, really, on how worried you are about these numbers. I'm not, particularly.

dougal



Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
PostPosted: Thu Jul 21, 05 3:36 pm    Post subject: Reply with quote    

cab wrote:
dougal wrote:
I'm a little surprised at the weight that can be attached to analysis of just *34* samples from the whole of the UK...
It's one of those things where the process is rather well characterised. ... based more on cell wall components than anything else, and as the chemistry of cell walls of Ascomycetes and Basidiomycetes ain't that different, in my view that would be overly picky. It doesn't matter whether there are 34 samples or 340 samples from the UK, what matters is that the samples are representative; you need to have enough (six would be nice) from each type of habitat you're most interested in, and this study concentrated on such habitats.


I read that as you saying that there should be *little* variation based on species, local geological mineralisation, micro-local or individual variability.
In my limited understanding of the subject, I understand that metal uptake is believed to be highly dependant on pH, and one doesn't have to be much of a gardener to know that soil pH is highly variable, both locally and regionally.
And anyway I've always found variability to be the bane of mushroom identification!
Quote:
Quote:

I must say I'd have liked to have seen some justification for their definition of "rural" sample sites as being "more than 20 metres from a road".
Given that definition, and the small sample size, I'm not exactly surprised that there should be no statistically significant differences between lead levels in urban, rural and rural roadside samples...
I don't get you. They need to use a definition, so they picked one that at least made some kind of sense. Proximity to a road is a fairly good one, because the specific pollutants they were looking for don't travel a great distance from roads before they get onto the ground, at which time they become bound to something very fast. These metal ions are like that.
ISTR that studies had found that lead from vehicle exhausts *did* travel quite a distance.
I have found a study that suggests that soil lead levels took 50m from a road to fall to background levels. And also speaks of clusters of extremely high blood lead levels in children, within the same city.
http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_44866.htm It wouldn't surprise me to find that there was some inverse square law relationship, but 20m seems awfully close, and I'm also of the opinion that traffic density would have a part to play, (at least in the peak roadside value) and hence the *type* of road should be defined. Its a bit loose and unhelpful as a definition IMHO.
So, I was not surprised that the individual *variability* was so great that it swamped any distinction between urban and "rural" (by that definition).
Quote:
Quote:
Personally, I think it sounds as though there is room for a study of how Arsenic concentration might vary, for example with distance from roads or with local geology.

That would indeed be interesting, but then again having a few samples being close to such limits (which are set well below any practical toxic levels) isn't something I would lose any sleep over.
Quote:
"Five of the thirty-four samples of fungi had lead concentrations higher than the legal limit of 1 mg/kg that would apply to commercial samples of fungi." (COT in the Annex)
If, as you believe, the sample *is* representative, then 15% of all wild fungi would be above the legal Lead threshold for sale.
If such a thing were to be discovered about any supermarket product - can you imagine the fuss that there would be?
And the response to official statements that these concentrations "do not provide any cause for concern for individuals eating these foods".

I am no toxicologist, medic or biochemist. I am not in a position to second guess the World Heath Organisation or the UN Food and Agriculture Organisation.
I don't know how "conservative" their recommendations really are.
But by their standards these numbers seem rather high.

And the clear message is that the distribution includes a lot of low levels, and a few rather high ones.
Which suggests, to me, that this report might be better construed as a call for more research, rather than giving a blanket "all clear".
And that a diversity of collection (species and sites) has to be a good thing.

Quote:
Quote:
...when calculating the exposure to these pollutants, they seem to reckon that only 2.5% of foragers would ever eat more than 27g (dry weight) of mushrooms in a day.

..eating an entire 25g packet of dried ceps on your own is pretty massive consumption; I've never got through so much, and I find if I put too much dried Boletus into a dish that it is very overpowering.
Isn't the reason for the popularity of (esp) Boletus edulis that it produces a powerful flavour? (So less would be used.) IMHO, there seems to be a distinct risk of exceeping the published limits, especially with concentrated preparations like ketchup made with less flavoursome species, especially if you happen to be unlucky enough to pick from some pollution hotspot.


Quote:
Quote:
IMHO, it would be more realistic to "weight" the average, based on the relative abundance of those species in foragers' baskets? (And yes, that will vary through the season.)

I can see where you're coming from with that, but lets look at the practicalities.
... I used to go home with a bag containing three dozen species. In Thetorf forest,.. about a dozen species. ...something like 30 species in my local woodland, ... As a rough guesstimate, I've picked and eaten over 200 species of mushroom.

Yes cab, but do you think you are typical?
From the radiocaesium paper:
"Consumption rates were recorded from 233 people, 80 per cent of whom ate less than 3 kg per year FW. The maximum intake recorded was 25.7 kg per year FW. 60 per cent of people only ate one species and this was usually the common field mushroom."
Or as I expect you'd agree: 'what they thought were field mushrooms' ...


The approach (of the report originally quoted by cab) seems to be to calculate the exposure of a person potentially eating large quantities of 'average' mushrooms.
My hypothesis is that the distribution of appetite, *combined* with the distribution in metal concentrations could well produce a distribution of exposures with a significant "tail" above recommended levels.

Accordingly, a variety of species, from a variety of trusted sites would be the prudent approach.
Unfortunately, one simply cannot taste or tell the heavy metal contamination of one's own basket.
But given mushrooms proven ability to mop up heavy metals from the environment (my reason for pointing out the "smelter" studies), it must be said that it clearly looks like a bad idea to eat mushrooms gathered from beside busy roads or from "the vicinity" (undefined) of industrial sites, or those with an industrial past.



Quote:
...we waved samples under a Geiger counter in Lancaster, and found that they crackled less than chellfish you could buy that were gathered in Morecambe bay; wasn't enough in them to worry me.
...
to avoid anywhere in the viscinity of industrial activity is harsh, I think, but again, if eating mushrooms from anywhere close to industry at all will worry you, don't do it. More left for me (yaay!)
Depends, really, on how worried you are about these numbers. I'm not, particularly.


I'm all in favour of people making their own *informed* judgements, based on their individual aversion to risk.
Without questioning the overcaution of the WHO or the FAO, my interpretation of these measurements is, like JB, to think that they are some way short of proving that the risk of heavy metal poisoning is negligable.
Although I love Mussels, I'm not sure that I fancy eating bivalves from *anywhere* round the Cumbrian coast... but I think checking them with a G-M counter wouldn't go down too well on most market stalls...
I'll accept a fair degree of risk, where I can feel that the risk is under my control. I'm much more averse to significant random risk, where skill or judgement has no part to play, and its down to simple blind luck.
In this case, unless you eat lots, or happen to pick contaminated specimens (not that you'd know it), it looks as though there ought to be more danger in excessive worry or misidentification. But if that report really is the best info, it suggests things are less clear than I had believed.

cab



Joined: 01 Nov 2004
Posts: 32429

PostPosted: Fri Jul 22, 05 1:05 pm    Post subject: Reply with quote    

dougal wrote:

I read that as you saying that there should be *little* variation based on species, local geological mineralisation, micro-local or individual variability.
In my limited understanding of the subject, I understand that metal uptake is believed to be highly dependant on pH, and one doesn't have to be much of a gardener to know that soil pH is highly variable, both locally and regionally.
And anyway I've always found variability to be the bane of mushroom identification!


That's all true, there will be variation in availability of such ions depending on pH and a number of other factors, but between similar sites I'd expect such variation to be limited to an order of magnitude or so (which, at such vanishing concentrations, matters very little).

[quote]

Quote:
ISTR that studies had found that lead from vehicle exhausts *did* travel quite a distance.


With something like an exponential drop in concentration away from the road. Or does it fall with the fourth root or something daft like that?

Quote:

I have found a study that suggests that soil lead levels took 50m from a road to fall to background levels. And also speaks of clusters of extremely high blood lead levels in children, within the same city.
http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_44866.htm It wouldn't surprise me to find that there was some inverse square law relationship, but 20m seems awfully close, and I'm also of the opinion that traffic density would have a part to play, (at least in the peak roadside value) and hence the *type* of road should be defined. Its a bit loose and unhelpful as a definition IMHO.
So, I was not surprised that the individual *variability* was so great that it swamped any distinction between urban and "rural" (by that definition).


While I see where you're coming from, there's still the factor that distance, the fact that drop off in concentration as you go away from the road, is likely to be at least exponential, meaning that the difference between 20m (definition used) and 50m (what you've suggested) seems likely to be trivial; were someone to be test that hypothesis, I'd be interested.

Quote:

"Five of the thirty-four samples of fungi had lead concentrations higher than the legal limit of 1 mg/kg that would apply to commercial samples of fungi." (COT in the Annex)

If, as you believe, the sample *is* representative, then 15% of all wild fungi would be above the legal Lead threshold for sale.


What of it? The legal limit and the actual safe limit, the kind of limit that would worry a toxicologist, are very different. More to the point, the amount of mushrooms you'd have to eat to get a significant amount of lead down your gullet over any meaningful period of time would me enormous. Put this into perspective, and it's just not something I'd worry about. Heck, you're suffering more dangerous pollution cycling through a town centre.

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If such a thing were to be discovered about any supermarket product - can you imagine the fuss that there would be?
And the response to official statements that these concentrations "do not provide any cause for concern for individuals eating these foods".


Yeah, there'd be some crazy panic like there was over Congo red, where tons of food that wasn't particularly dangerous was dumped; fair enough, most of it was crap, but that there would be a food scare doesn't justify that said food is in any way really dangerous. Heck, there'd be a lot less food scares if food had to really be dangerous to cause one

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I am no toxicologist, medic or biochemist. I am not in a position to second guess the World Heath Organisation or the UN Food and Agriculture Organisation.
I don't know how "conservative" their recommendations really are.
But by their standards these numbers seem rather high.


They don't especially worry me; I'd refrain from eating mushrooms from right by a busy road or a site that I had good reason to doubt, other than that I'm still not fussed.

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And the clear message is that the distribution includes a lot of low levels, and a few rather high ones.
Which suggests, to me, that this report might be better construed as a call for more research, rather than giving a blanket "all clear".
And that a diversity of collection (species and sites) has to be a good thing.


I'd say that diversity of species utilised and collection sites is a good thing for all sorts of reasons, including conservation, gastronomy, interest and intellectual satisfaction. I'd say that should be the goal of any forager. Safety comes down the list there for me, but if such makes anyone safer, great.

Quote:
Isn't the reason for the popularity of (esp) Boletus edulis that it produces a powerful flavour? (So less would be used.) IMHO, there seems to be a distinct risk of exceeping the published limits, especially with concentrated preparations like ketchup made with less flavoursome species, especially if you happen to be unlucky enough to pick from some pollution hotspot.


Ketchup doesn't concentrate down anything like as much as drying, and I'll wager that most of the metal ions would be left on the solids rather than being in the ketchup (they'll stick to charged sites on the chitin cell walls; even the most 'chitin' of chitins will have some deacetylated sites, which are the charged sites most likely responsible for holding on to the metal ions).

While there's a theoretical risk of people eating way more dried mushrooms than I can possibly stuff down my guests thoats when trying to clear up some cupboard space, it seems like something that you couldn't do often or easily.

Quote:

Yes cab, but do you think you are typical?


I like to think I'm fairly atypical; where's the fun in being normal?

But I'm not so far from being typical. Many pickers consume a LOT more species than they think they do, especially those who pick Russula and Boletus, not to mention those who have trouble separating out, say, different species of Agaricus.

Quote:

From the radiocaesium paper:
"Consumption rates were recorded from 233 people, 80 per cent of whom ate less than 3 kg per year FW. The maximum intake recorded was 25.7 kg per year FW. 60 per cent of people only ate one species and this was usually the common field mushroom."
Or as I expect you'd agree: 'what they thought were field mushrooms' ...


Indeed But that still leaves 40%.

I've got a theory about British mushroom pickers and how habits in the UK have changed two or three times, remind me to share it some time.

Quote:
The approach (of the report originally quoted by cab) seems to be to calculate the exposure of a person potentially eating large quantities of 'average' mushrooms.
My hypothesis is that the distribution of appetite, *combined* with the distribution in metal concentrations could well produce a distribution of exposures with a significant "tail" above recommended levels.


I suspect that there could indeed be some few people, who eat from heavily contaminated sites, and who eat masses and masses and masses of wild mushrooms, could indeed be getting over the reccomended concentrations of metal ions in their diet. I also suspect that very few of those would be getting to an actually toxic level of such ions.

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Accordingly, a variety of species, from a variety of trusted sites would be the prudent approach.
Unfortunately, one simply cannot taste or tell the heavy metal contamination of one's own basket.
But given mushrooms proven ability to mop up heavy metals from the environment (my reason for pointing out the "smelter" studies), it must be said that it clearly looks like a bad idea to eat mushrooms gathered from beside busy roads or from "the vicinity" (undefined) of industrial sites, or those with an industrial past.


I'd agree that avoiding sites of known contamination would be a good idea. But then again, such sites do tend to be recognisable (you get odd vegetation); really, I think that few mushroom pickers (who HAVE to be cautious if they're to be long lived!) are going to manage to poison themselves this way.

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I'm all in favour of people making their own *informed* judgements, based on their individual aversion to risk.
Without questioning the overcaution of the WHO or the FAO, my interpretation of these measurements is, like JB, to think that they are some way short of proving that the risk of heavy metal poisoning is negligable.


I don't think that they set out to prove that; what I like about the study, and the reason why I often quote it, is that all the numbers are there for dissection. It was the subsequent opinion of the authors, it would appear, that there's not a lot to be concerned about. I share that opinion, but I'm quite happy (delighted, in fact) if others decide to be more concerned about it. More left for me

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Although I love Mussels, I'm not sure that I fancy eating bivalves from *anywhere* round the Cumbrian coast... but I think checking them with a G-M counter wouldn't go down too well on most market stalls...


I used to gather cockles on Morecambe bay. I often went out after the tractors, the chaps raking up the cockles not really minding having someone tagging along behind in a pair of army boots and shorts, with his own bucket. I probably took in a fair whack of radioactive material from that mud and from the cockles; my biggest risk, in fact by far the greatest risk I suffered, was gettin sucked down into the mud. So I always followed a local

My point here is that such risks should be kept in contxt; I wouldn't pick winkles from so close to Hartlepool nuclear powerstation as I used to (my mum made me when we were on holiday in a caravan at Crimdon Dene!), but I'd always weigh up the risks and compare them to the risks we face all of the time anyway.

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I'll accept a fair degree of risk, where I can feel that the risk is under my control. I'm much more averse to significant random risk, where skill or judgement has no part to play, and its down to simple blind luck.
In this case, unless you eat lots, or happen to pick contaminated specimens (not that you'd know it), it looks as though there ought to be more danger in excessive worry or misidentification. But if that report really is the best info, it suggests things are less clear than I had believed.


I would tend to think that the worst risk found in that study doesn't look like a risk that worries me too much. While there's ALWAYS room for more information, my best bet here is that there's little to worry about if you're willing to use your head a bit.

dougal



Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
PostPosted: Fri Jul 22, 05 2:41 pm    Post subject: Reply with quote    

So, summarising, I think we can agree that one should:-
- NOT pick mushrooms at or "close to" the roadside
- NOT pick mushrooms "in the vicinity of" industrial or post-industrial sites
- NOT eat "unusually large" quantities of wild mushrooms, especially similar species from the same site

...because mushrooms are rather good at picking up heavy metals from the environment.

The definitions of the terms in quotes above are a matter for personal risk assessment.

By observing these guidelines, there is only a very small residual chance that (by eating wild fungi) one might occasionally exceed published guidelines for heavy metal consumption - however, it is believed that any such occasional small exposures are extremely unlikely to be harmful.

monkey1973



Joined: 17 Jan 2005
Posts: 683
Location: Bonnie scotland
PostPosted: Fri Jul 22, 05 2:55 pm    Post subject: Reply with quote    

Nice one dougal. Saved me a lot of reading there.

tahir



Joined: 28 Oct 2004
Posts: 44302
Location: Essex
PostPosted: Fri Jul 22, 05 2:57 pm    Post subject: Reply with quote    

Love the Orangutan, reminds of one of my daughters

cab



Joined: 01 Nov 2004
Posts: 32429

PostPosted: Fri Jul 22, 05 3:03 pm    Post subject: Reply with quote    

dougal wrote:
So, summarising, I think we can agree that one should:-
- NOT pick mushrooms at or "close to" the roadside
- NOT pick mushrooms "in the vicinity of" industrial or post-industrial sites
- NOT eat "unusually large" quantities of wild mushrooms, especially similar species from the same site

...because mushrooms are rather good at picking up heavy metals from the environment.

The definitions of the terms in quotes above are a matter for personal risk assessment.

By observing these guidelines, there is only a very small residual chance that (by eating wild fungi) one might occasionally exceed published guidelines for heavy metal consumption - however, it is believed that any such occasional small exposures are extremely unlikely to be harmful.


That's not such a bad summary...

The only thing I'd add is don't worry about it too much. You are more likely to make yourself sick with worry than sick with pollution on your wild food, unless you're really dumb and pick from a heavily contaminated site.

joanne



Joined: 28 Oct 2004
Posts: 7095
Location: Morecambe, Lancashire
PostPosted: Fri Jul 22, 05 3:14 pm    Post subject: Reply with quote    

tahir wrote:
Love the Orangutan, reminds of one of my daughters


What does that say about your offspring ?

Poor kidlet

Jo

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