AusBonsai

following on from the thread viewtopic.php?f=12&t=14901&view=unread#unread...

63pmp wrote:Be very careful using galvanized trays to collect runoff/leachate. The zinc released can become toxic to your plants. Especially if you have acidic soils/runoff/fertilizer.

Paul

Ok, thanks Paul, mostly the runoff gets used on other (less significant) pot plants, I also use a lot more organic 'ferts' (like Seamungus) something to watch for I guess, I'll avoid using it on the vegies too. Might see if I can come by a cheap water testing kit?

A few questions though Paul, I hope you don't mind answering:

• Hoping that the fact that the runoff doesn't 'sit' in the trays, rather it flows through them, may help?

• Does amount of zinc released dissipate over time i.e. once they are weathered in?

• Is this a factor for anyone collecting roof rainwater that has uncoated guttering?

• And, lastly, what metal would you get them fabricated in?

Pup, what are your trays made from?


Thanks Paul, and Pup
Cheers, Ryan

Interesting topic and one i reckon could create some lively discussion.
I for one do just that as i have Gal iron roofing under most of my benches to collect runoff. I have done so for 8+ years now
viewtopic.php?f=29&t=1404&hilit=+runoff

Another thought is that just about every farmhouse has (or used to have) Iron roofing and rainwater tanks. I have never heard of it being an issue before.

Also not forgetting that just any tin can on the supermarket shelves would have the same problem. I know i have had tinned food on the shelf for 5 years and consumed it with no ( obvious ) concern.

Ken

kcpoole wrote: Another thought is that just about every farmhouse has (or used to have) Iron roofing and rainwater tanks. I have never heard of it being an issue before
Ken

I agree with you to a certain extent Ken as I was reared on rainwater off a roof in Sydney in the 1950`S (yes I know I am an old Bugger) but rooves didn`t have concentrated chemicals tipped over the every day?week whatever your fertilising regime is,so it could be a concern.
Paul

yeah, bollocks. there is no toxic problem with zinc or galvanised iron.

A zinc concentration in the range of 2-3 mg/L will cause toxicity in plants if used regularly. General hydroponics recommendation for continuous feeding is in the range of 0.05 - 0.1 mg Zn /L. Typical guidelines for zinc content in irrigation waters is a max of 1 mg/l to soils with pH less the 6.0 (acidity affects availability of zinc to plants), to 5mg/l with pH >7.0 ((ref: http://www.env.gov.bc.ca/wat/wq/BCguide ... /zinc.html ) 1000ug/l = 1mg/l))

It is not uncommon for zinc levels in rain water tanks connected to zinc gal roofs to be in the range of 3-11 mg/l ( ref

My reference

Lead and other heavy metals: common contaminants of rainwater
tanks in Melbourne
M.I. Magyar1, V.G. Mitchell1, A.R. Ladson1, C. Diaper2
1Monash University, Institute for Sustainable Water Resources, Department of Civil
Engineering, Victoria 3800, Australia
2CSIRO Integrated Urban Water Systems, Graham Road, Highett, Victoria 3190, Australia
ISBN 0-858-25735-1 © 2008 publication: Water Down Under 2008


The general toxicity to humans in is in the order of hundreds of mg/L, though too much will make you sick.

It is quite possible for the zinc concentration from galvanized roofs, and reticulated water systems using galvanized iron to develop a level that is toxic to plants, yet have no effect to humans. Once again, "if you can drink the water, then it is OK for your plants" is a complete myth.

It is better to use colorbond iron ware.

The cans used for food storage are lined with tin not zinc, this can corrode and can cause illness in people. Don't eat any food from a can that has rust in it or is bloated or swollen.

This is from wikipedia, so its not the best of references, but it will do. Type in "tin can" for a history of the tin can.

Dissolution of the tin coating into the food

Although tin is corrosion resistant, acidic food like fruits and vegetables can cause corrosion of the tin layer. Nausea, vomiting, and diarrhea have been reported after ingesting canned food containing 200 mg/kg of tin.[9] A 2002 study showed that 99.5% of 1200 tested cans contained below the UK regulatory limit of 200 mg/kg of tin, an improvement over most previous studies largely attributed to the increased use of fully lacquered cans for acidic foods, and concluded that the results do not raise any long term food safety concerns for consumers. The two non-compliant products were voluntarily recalled.[10]

Evidence of tin impurities can be indicated by color, as in the case of pears, but lack of color change does not guarantee that a food is not tainted with tin.


Paul

Some plants are more susceptible to zinc than others. Zinc poisoning was pointed out to me at Mt Buffalo. Where gal posts have been used around viewing platforms the mosses and lichens are gone from the rock face directly below each post leaving bare streaks down the granite rockface.
Humans in many areas are zinc deficient. Some testing done with nursing mothers found many were quite low in zinc. Trials found babies sleeping better while the mothers take zinc supplements.

Brian wrote:yeah, bollocks. there is no toxic problem with zinc or galvanised iron.

Yeah bollocks aye, you tell that to my vet,after my dog drank some of my runoff fertiliser collected in a a galvanised bucket ,all I got was a $800.00 vet bill and a dead dog .so I would rather believe the vet and the other Paul.

PS And the galvanising was starting to etch away the coating up to the fertiliser level,so in my know nothing opinion,I would say it aint real good for you or your plants

Zinc can help with some colds. But it can also cause a permanent loss of smell, so take your pick there.

Ok so it looks like Galv trays may cause some issues in the long run especially when fertilisers are introduced.


Rather than debating whether it is or isnt a hazard for plants I would like to know what safe alternatives are out there.

My ex was always on my back about water wastage from watering and I would like to do my bit for the environment and my pocket (with SA water prices) by re-using as much as possible

And Paul W, Im sorry to hear about your dog, but do you think it may have been more likely contamination from the fertiliser rather from Zinc? Im not wanting to start a debate, I was just raising the question as I wouldnt think either would be healthy for any animal

if you are really that concerned about zinc poisoning of your plants, then you can brush a coat of black rubber membrane to the tray. I'm referring to the stuff that they use to waterproof fishponds. Its non toxic.

Gee, thanks all for your input. Doesn't sound like a huge problem in my case, I've also noticed too there is now a layer of silt build up which maybe minimises/negates any erosion of the zinc layer? Not being a chemist, just wondering too if runoff, left to settle in a plastic drum, would the allow the zinc to drop out? or maintain suspension?
Some interesting points of view and personal experience.

Cheers, Ryan