Found a quote in a Swedish newspaper about citrus and I would be surprised if it was true. (Sweden is of natural reasons not the top citrus growing country). It said that:

"You should not eat citrus from trees bought in flower/garden shops but only use them as ornamental trees. The reason was said to be the use of long term active anti-fungus pesticides that was not good for your health."

Most of the Swedish citrus trees sold are grown in green houses in Denmark, Netherlands or Germany I would think, if not imported from Portugal, Spain or Italy.

Have anyone heard of such treatment and for how long could the pesticide stay in the tree/fruits?

The newspaper article has an ounce of truth and a pound of error. Commercial citrus fruit is coated with a funguscide plus a wax coating, This is done to protect the fruit's freshness. This coating is only on the rind of the fruit which is, of course, peeled and thrown away. Billions and billions and even more billions of people have been eating this frulit without any harm for a long tme. Some people have even eaten the rind with out any harm. Small citrus trees sold through nurseries, garden centers or greenhouses are NOT coated with a fungicide nor the wax. There is NO danger in any case. - Millet

Thanks Millet!
it did sound strange.

Agree, sounds like it means systemic fungicides and pesticides used in the production of ornamental trees at flower shops etc, any fruit on your new tree will also contain the chemical.

Garden centers is a common seller of regular citrus trees. At least here in the USA. I purchased many of my trees at garden centers. - Millet

Yes,
systemic fungicides in imported decorative citrus plants,
sorry if I did a poor job in explaining.

How long could these stay in the trees and the new fruits.
(I have replanted all in new soil after buying the plants)

I do not know about fungicides but noticed an abberrant growth/flowering habits in the potted Dutch citruses. For me it lasted about one year. Probably some retardants were being used.

It may have something to do with ornamental plants not being food for human consumption, where there are controls on maximum residue levels, witholding periods before treated produce can be harvested, or even allowable chemicals in the different production systems.
Maybe plant nurseries dont have the same controls as food producers, so ornamental fruit plants not required to meet the same standard.

How long do the chemicals last ? Would vary according to the chemical, and the period of effective control after application, plus a bit more as they fade away.
Natural Pyrethum gives days to a week control of leaf miner, systemic insecticide can give several weeks at least.

Is this such a big issue, compared to other chemicals in food, or post harvest treatments for exported fruit ?, or even some common household chemicals or DIY projects using heavy duty cleaners ?

Found this thread on the subject,
seems to agree with the comments here,
many thanks for the help!

http://www.growfruitandveg.co.uk/grapevine/feeling-fruity/aldi-lemon-tree-says-not-consumption-true_55359.html

My two cents worth. These days a farmer is guilty until proven innocent. There are some dangerous things that get imported into the US but most of the bad stuff gets caught. Dangerous fish and shrimp full of illegal chemicals from over seas comes to mind. Many years ago a complete idiot used Temik on some watermelons. He never got caught but Temik had no value as a pesticide in melons that I know of. It wasn't labeled for melons either. It was a very dangerous chemical and it was abused by an idiot. I read that some other idiots used it as roach poison and as a rat poison in their homes. They got sick and some of them died. It is very deadly stuff. Now nobody can use it. I think it is completely off the market. Probably a good thing too. We need some safeguards against idiots. They seem to be everywhere. Tom

I use a systemic fungicide by the name of Banrot 40WP on my newer trees that I know that I will not be harvesting fruit from for quite some time as a precaution against rootrot that would result from improper culture during the time it spent with the vendor that I bought it from.. I understand that this product is commonly used on ornamentals in a greenhouse environment to control the control of damping-off, root
and stem rot diseases caused by Pythium, Phytophthora, Rhizoctonia,
Fusarium, and Thielaviopsis.. The active ingredients in Banrot 40WP are Etridiazole and Thiophanate-methyl. It is soil applied. The product label notes a 2yr period between application and harvest for bearing citrus.

If you're concerned that some of your potted citrus has been treated with such a product prior to your ownership and wanted to stay on the safe side, I'd consider a 2 year grace period between the time you take possession of the tree and ingesting the fruit from it. This actually works out well given the recommendation to strip young trees of fruit for the 1st couple of years to encourage canopy and root development.

Product label here: http://everris.us.com/sites/default/files/h4801_banrot_40wp_specimen_label_120312.pdf

Best,

Skinn30a