In Florida, early grapefruit varieties were induced to bear earlier by spraying the fruit with arsenic to induce peel injury, and thus ethylene production, this was one of the best kept secrets of the grapefruit industry.

Millet (1,289-) Susan B Anthony List - Washington DC

Millet, I think the actual compound used was lead arsenate. When it was banned, growers were allowed to use up any remaining stock they had on hand.

Let's see, what could we use to ripen grapefruit. I know, let's use a lead compound. No, better, let's use an arsenic compound. Even better, let's use a compound that includes both. As neither lead nor arsenic has ever been shown to be harmful, I have no idea why this compound was pulled.

A bit more history, and a bit of physiology.

Lead arsenate was first used in the 1920s, to control an outbreak of Mediterranean fruit fly. In that campaign, it was noticed that trees sprayed in the spring produced less acid in the fruits, and they therefore matured earlier than those on unsprayed trees. So growers began to use the material for maturity management.

The Florida Citrus Code of 1949 (which, as amended many times, is still the "law" for citrus in Florida) banned the use of all arsenating substances on citrus, but then there was a special amendment passed, forbidding the enforcement of that law, specifically and uniquely on grapefruit with lead arsenate. It specifically exempted the lead salt, not any other form of arsenate.

When I started teaching citrus in the early '80s, we were still using it, only for early season grapefruit. I wouldn't call it a secret -- it was a standard production practice. Because it was used only in the spring, while the fruit was still quite small, and because it is not well-absorbed into the fruit, by harvest time, lead and arsenic levels had dropped far below the FDA's safety limit, so it was legal to market.

I have never heard that it injured the peel and/or produced ethylene, nor can I see how that would have any effect on acid content inside the fruit. I think that reference is in error. That would describe the desired effect of an abscission chemical, but not the arsenate effect. What's actually going on there is that arsenate blocks one of the enzymes in the Krebs cycle (a.k.a. citric acid cycle) at that time in fruit development when citric acid would normally be being diverted out of the cycle, to add acid to the fruit. So the fruit never acquires a normal amount of acid. In an untreated fruit, the tree ships sucrose (regular table sugar) from leaves (where it's made by photosynthesis) into the developing fruit. Once there, Krebs cycle would be the normal route of respiration, same as we use when we break down carbohydrates into carbon dioxide, water, and energy. But in a fruit, the process stops at citric acid, rather than going all the way to CO2. Hence, the citric acid content increases dramatically. That's what we're blocking. Any existing acid is unaffected, so the date of the spray can control how much earlier the fruit will mature.

Because of the odd working of the law -- banning it and then forbidding enforcement on grapefruit, there needed to be some protection for oranges, to keep them from being sprayed, either on purpose or accidentally (drift from an adjacent block of grapefruit). Hence, the clause in the orange maturity law that demands a minimum 0.4% acid content, to be legal for sale. We still have that clause, although it is often ignored, especially for early fresh fruit, most notably navels, which often don't have quite that much acid, yet taste very good anyway.

I think it safe to say that no arsenate use has happened in the last 20 years or more, because its effect on acid is so dramatic, one would be caught immediately by the packinghouse inspector, who would notice that your grove block's acid content was less than that of surrounding growers' fruit.

As for health danger -- remember that at that time, leaded gasoline was being used, and I seem to recall seeing numbers somewhere (sorry, don't know where now), showing that the amount off lead one could get from eating arsenated grapefruit was far less than the "normal" dose from breathing car exhaust on the highway, even if you ate the peels. Lead always was the entity of greater concern.

I wonder what the lead and/or arsenic impact to the soil would be from all that spraying way back when? An awful lot of houses built on former citrus groves now.

.....Alan.

The reference to the grapefruit's injured peel caused by the spraying of arsenic and thus producing ethylene, comes from the University of Purdue's educational lecture series. Particularly from Lecture # 32.

Millet (1,388-) Susan B Anthony - Washington DC

The Purdue folks are apparently mistaken here. Ethylene would promote the fruit falling from the tree, and perhaps early color formation, but should have no effect at all on internal quality, and certainly, not in reduced acid formation early in the season. The mode of action I described is, as far as I know, completely accepted by all citrus physiologists.

Malcolm

Alan, The total Pb and As amounts would be quite small, I think, even over many years, but yes, whatever was sprayed is likely still there in the top few inches of soil, since they'd be tightly adsorbed and not easily leached away. On the other hand, we have an ongoing problem with vast amounts of copper in the soil from years and years of its use as a fungicide. Again just in the top few inches of soil, but in some cases, well over 50 lbs per acre-inch.

sorry for the typos. Should proof read better! till=still, above, and "come cases" should read "some cases."
MM

Lead is much more of a concern to women and children and can cause developmental defects at levels as low as 40 micrograms/day in children if I remember correctly.

Arsenic replaces phosphate on many biological processes and when it replaces the P in ATP it often decomposes without supplying the energy needed for reactions.

Dr. Manners, in reading your post, I can easily see your reasoning concerning ethylene gas causing the process of abscission. I feel your interpretation is the correct one. Below, I have cut and pasted the section from the Purdue lecture concerning the matter. They must be mistaken.

....."In Florida, early grapefruit were induced to bear early by spraying with arsenic to induce peel injury and thus ethylene production, one of the best kept secrets of the grapefruit industry.".....

Thanks for clearing it up.

Millet (1,299-)

"Ethylene would promote the fruit falling from the tree, and
perhaps early color formation, but should have no effect at
all on internal quality, and certainly, not in reduced acid
formation early in the season. The mode of action I
described is, as far as I know, completely accepted by
all citrus physiologists."

That is how I learned it with Fruit & Nut trees. For Apples
however the gas can affect the internal quality of the fruit.
The pulp can become a little softer, less firm, mushier
along with the advent of the production of natural ethylene
which is a natural occurring degradation gas which leads
to an overripe condition in many but not all Apples as an
example. For some Apples ethylene was used as a
late season "growth regulator" spray to help sugar up
some of the spur type Apples but they had to be shipped
and/or in the stores fast soon after the application.

Ethylene gas was used in select packinghouses out
here to induce a softening to the pulp and rind of the
hand picked fruit. The feeling was that once the gas
entered into the pulp, some of the acid content would
be neutralized giving the impression that the treated
fruit were sweeter than the untreated fruit were. Not
everyone felt this type of treatment was beneficial
but the process did have some marginal to adequate
results with early picked (November and December
ripening but not necessarily mature) Navel Oranges.
As a side note: the mature Navel Oranges years ago
were not good fresh market shippers and stayed pretty
much close to home.

For white and amber fleshed Grapefruit in Southern
California years ago ethylene treatments did help
produce a seemingly (not sure if the results were
ever properly studied and tested to know for sure)
less acid content fruit for retail sales. Cannot speak
for the Pink Grapefruit as people in Texas are better
aware of what went on there with them than me for
their fresh market fruit.

Millet, years ago there was not the concern of
fruit falling to the ground in Florida and being
used for juice and processing. For us here
with our markets in fresh market fruit much
of the fallen fruit had to be discarded. Wasn't
worth it to us to even pick up the fallen Navel
Oranges and toss them into the field cartons
as it cost us more to have the fruit processed
or go for juice than we got back in premiums.
Out here we could not compete with Florida
in this respect and for a number of years none
of the Navel Orange growers tried to compete
in the juice and processed market. As I
remember it, ethylene was not used as a
standalone treatment in groves too often.
Ethylene was used in conjunction with another
chemical or hormone additive in the formulation
out here for experimental grove applications.
I know of ethylene and an enhanced Bordeaux
spray having being used together in the distant
past for Citrus but this was light years ago or it
seems that way to me now right offhand.

Jim

Snickles, it is interesting how different climates can affect the effect of a chemical. In Florida packinghouses, we've "degreened" most of the citrus harvested before the 1st of January (about 40% of the fresh-shipped crop) for many years. And while ethylene treatments do result in much better color on our fruit, they do not normally affect softness nor any aspect of internal quality (brix, acid, ratio, etc.)

Ethaphon, a material that can be sprayed onto trees, and which then releases ethylene on exposure to sun and air, has been trialed as a harvesting agent, in that it loosens the fruit, making it easier to pick, but it never became commercial, so is never actually used. One of its big problems was that it also removed leaves, flowers, and (if present), next year's crop. oops.