Clam shells

[Mojave]

A couple of weeks ago I visited one of the local reservoirs and due to the low water level I was able to gather a good size bag of freshwater clam shells, I think they're clams anyway. I am moving soon and want to start preparing my new patch of ground for the Spring 2013 growing season. I'm hoping broken up clam shells will provide a natural source of slow release calcium.

Here's the problem. Uvas Reservoir is notorious for it's high levels of mercury (due to past mercury mining in the area) and there are warnings posted about pregnant women are not to eat the fish at all and everybody else severely restrict the amount of fish they eat from the reservoir. Does anyone know if shellfish can absorb mercury into their shells? I'd really hate to import some toxic heavy metal into my future garden.

[Lcottomsvcs]

Everything I have ever read about mercury bioaccumulation focused upon the levels present in the muscle tissue of the organism. I can't find anything about mercury content of shells.

[Mojave]

Originally Posted by Lcottomsvcs

Everything I have ever read about mercury bioaccumulation focused upon the levels present in the muscle tissue of the organism. I can't find anything about mercury content of shells.

That's about all I could find too. I think I'll ask our County Cooperative Extension experts.

Thanks for the reply, I'll let you know what they tell me.

[Crandrew]

i would stay clear of it. I would rather spend a few bucks to buy the crab shells than risk some mercury in my system. But thats just me.

[chancethegardener]

Neptune's Harvest crab shells is a perfect product to add Ca to your soil.

[Mojave]

Well I got a non-answer from the Cooperative Extension. I thought it would be really cool using a free and native/natural element in my garden.

Oh well.

[dice]

Try a University oceanography department. They would know.
http://ocean.stanford.edu/su/
Chris Francis maybe, if you can find his email address. It sounds
like something he would know off the top of his head, even though
his research area is marine rather than freshwater environments.

[bower]

Bill, although the levels of contaminant metals are lower in shell than in tissues, it seems likely that there would be some accumulation if there's a lot of mercury in the environment. Shells are made of calcium ion (Ca++) and several other metals including mercury have the same 2+ ionic value and therefore may well be assimilated in the shell building process. If I were you, I would not risk it in your garden.

I also have incorporated a lot of shell into my garden (mainly mussels), although as a source of calcium, I think it is really really slow release... maybe never! In fact archaeologists have traced some of the camp sites of native peoples who were living here hundreds and thousands of years ago, by the shell middens they left at those sites.... The shells may be more durable than plastic.

[Mojave]

Thanks Bower. I'm beginning to think spending a few bucks on a sure thing is better than taking chances.

Oh well. was worth thinking about.

[cmarchan]

I agree that the amount of mercury in the shells would be absolutely minimal for the reasons stated above. I think the length of time it takes for the shells to break down depends on a number of factors such as annual rainfall accumulation, soil ph, rain ph, till vs no till and maybe more. Out soil ph is often near 4.0! Being close to the salt, my family has always added copious amounts of clam shells (we eat a lot of clams)into the garden every year. The garden was always bountiful. We usually crushed them a bit first with a hammer or whatever was close by. I know there was dissolution because of the smooth and rounded appearance of the shells. I also remember a lot of broken beer bottle glass in there too Now, If I wanted to correct a calcium deficiency I too would opt for a commercual product (in addition to the clam shells).