A recent case history illustrates an important principle of mould control in tanneries.

A bovine wet blue tannery was using sodium mercaptobenzothiazole (MBT) as fungicide. They experienced a mould outbreak on this treated material. Samples of mouldy wet blue were passed to both George Halligan and myself.

Initially we thought it might have been an outbreak of Trichoderma, since the mould appeared to be green, and because this mould has caused a lot of problems in the past. However when cultured, it turned out to be a white colony that did not look at all like Trichoderma.   Under the microscope, it appeared, in fact to be a species of Penicillium.

We decided that we had to see what chemicals would, in fact control this specific fungus.  A simple minimum inhibitory concentration (MIC) test would be done.  In the end we carried out two of these tests.  This shows the smallest dose of fungicide that, in culture medium, will significantly kill, or at least slow the growth, of the mould.  Results are shown below.

Products and results are :
1.   50% carbendazim   10 parts per million
2.   30% TCMTB  40 parts per million
3.   50% Na MBT  160 parts per million
4.   45% phenol blend  160 parts per million

A small digression at this point may be in order.  George and I have several times been asked to look at mould samples, and identify the fungus.  Neither of us are qualified to perform a detailed identification.  Like others in other chemical companies and LASRA staff, we do our best to decide the genus from cultures and microscopic examination.  This is always a bit hit or miss.  For example, Penicillium is perhaps the most common genus of mould.  However, there are at least three other genera I am aware of that are almost indistinguishable from it under a normal light microscope.

In addition, Penicillium has, believe it or not, about 20,000 different species.  In consulting with one of New Zealand’s most qualified mycologists (PhD level), I was told that there is only one man in Australasia who is qualified to identify Penicillium down to species level.  He would take about three weeks to do it, and charge at least $ 5,000! Recent DNA testing shows that what we called Trichoderma viride is, in fact, over 100 different species.

Unless you identify a problem mould down to species level, it is probably of academic interest only.  Even then, the practical value is debatable.  Are you prepared to spend $ 5,000 plus, and wait a month or more to gain information of dubious  practical value?

Moulds are ubiquitous.  This simple sentence reflects the enormous prevalence of moulds in our environment, and particularly the mind boggling presence of mould spores everywhere.  The air around us is full of spores.  Every breath we take involves inhaling thousands of spores (nearly always harmless, fortunately).  However, the nature of these spores changes over time.  From season to season, and day to day, the mould species represented in these spores changes drastically.  A minor change in the local environment such as a pile of rubbish being left nearby may lead to an enormous increase in certain moulds.

The end result is that your wet blued leather is being challenged by a changing arsenal of moulds.  What attacks today is not what attacks tomorrow.  The mould control treatment that worked well yesterday may not work well today.

It is vitally important that the fungicide or fungicides that we use cover as broad a spectrum of mould species as possible.  It is for this reason that George and I have been working on carbendazim as an additive.  We were looking for an inexpensive material with high potency against the kinds of moulds that traditional fungicides might be weak against.  In particular, we wanted a product that would control Trichoderma really well.

Some of the initial work carried out, I discussed last year at this conference. I would now like to show you some of the results achieved since.

The following are all results, checked in the tropical chamber, of field trials in New Zealand.
In each case below,

TCMTB = 30% emulsifiable concentrate
MBT = 50% sodium mercaptobenzothiazole
Carbendazim = 50% wettable powder

1. A wet blue bovine tannery.

2. A wet blue bovine tannery # 2

 3. A wet blue bovine tannery # 3

With a higher dose of MBT, results are much better.  However, a small addition of carbendazim while lowering the MBT dose an equivalent amount gives even better results.

4. A vegetable tannery

In the more difficult task of protecting wet vege tan leather, a high level of TCMTB plus a high level of carbendazim does an excellent job.  Phenolic blend or TCMTB alone give much poorer results.

 5. A wet blue ovine tannery

6. A fellmongery – ovine pickled pelts #1.

Though the last two treatments cost no more than 0.04% of the 30% TCMTB, they are much more potent with a little carbendazim.

 7. A fellmongery – ovine pickled pelts #2

Again, a little carbendazim to replace one third of the more expensive TCMTB product actually increases performance.

In fact, after running numerous trials, we have yet to find a single set of trial results in which a little carbendazim does not add benefits to cost, performance, or both.

Adding up

1. the need to have as broad a spectrum fungicide as possible to cope with the inevitable appearance of new mould species
2. the need to enhance fungicide potency
3. the need to keep costs as low as possible