Tridemorph is a systemic fungicide that first gained commercial clearance
in 1969(1). An evaluation document to be published later in the year by the UK's
Pesticide Safety Directorate (PSD) will report concern over its potential
reproductive effects on spray operators. Until recently there has been very
little human health and environmental information in the public domain on this
active ingredient, yet it is used widely over numerous crops in many countries
around the world.
What is tridemorph
It is used to control the fungus Erysiphe graminis
in cereals, Mycosphaerella species in bananas, and Caticum
solmonicolor in tea. Tridemorph is formulated with the fungicide
carbendazim, to extend its spectrum of use in cereal disease control(2). It is
also used with a number of other fungicides including: cyproconazole,
fenbuconazole, fenpropi-morph, flusilazole, propiconazole, tebucon-azole,
Tridemorph is applied onto many crops
across the world, but very little data on usage and production is in the public
domain. It was developed in the 1960s by the German multinational BASF who sell
tridemorph under the trade name Calixin. In Europe, it is used in Austria,
Belgium, Finland, Germany, Greece, Italy, Ireland, Luxembourg, Netherlands,
Spain and UK(4). It is applied
widely on banana plantations Latin America, especially Costa Rica and Ecuador(5).
In the UK there are 29 approved
products, predominately for use against powdery mildew on cereals but also on
root crops. There are no home garden products(6).
In 1997, tridemorph was most commonly used on winter barley (61,207 kg) followed
by wheat (50,588 kg) and spring barley (18,411 kg)(7).
The acute oral LD50 (the dose required to kill
half a population of laboratory test animals) for tridemorph is 650 mg/kg for
rats. It is classified by the World Health Organisation as Class II a
'moderately hazardous' pesticide(8). It is harmful if swallowed and irritating
to eyes and skin(9). Tests show it is moderately to severely irritating to
rabbit skin and rabbit eyes. Prolonged or repeated exposure may cause dermatitis
and/or conjunctivitis. Inhalation of tridemorph vapour may cause adverse health
effects (specific effects not stated). Laboratory rats survived an 8 hour
exposure to air saturated with tridemorph vapour(10).
Until recently, very little data was in the
public domain. On 19 March 1999, Jeff Rooker the UK Agriculture Minister
announced that the use of tridemorph would be restricted due to concerns over
its reproductive effects. PSD, an executive agency of the Ministry of
Agriculture, Fisheries and Food (MAFF) has considered the data under the UK
Review Programme, and will produce a full evaluation later in the year. The
Advisory Committee on Pesticides, which advises UK Ministers on pesticide
safety, considered PSD's review of tridemorph in February 1999 and made a number
of recommendations (see below)(11).
Ministers and officials at MAFF became
concerned after BASF, the main manufacturer of tridemorph, provided new
information that identified a possible risk of harm to the unborn child if the
mother is exposed to tridemorph while working with the chemical. The company
submitted its data as part of its obligation under the Food and Environment
Protection Act 1985 to provide any new information on the potentially dangerous
effects of a pesticide product. The data comprised developmental toxicology
studies in the rat and rabbit, and a literature review of developmental studies in
vivo and in vitro.
PSD assessed these studies and
concluded that tridemorph was capable of inducing abnormalities, primarily cleft
palate, during the development of the rat foetus. In rabbits, it did not appear
to be teratogenic. Scientists at PSD consider this difference was not addressed,
and from the available information, it was not possible to determine whether the
effects seen in rats would be produced in humans. They were nevertheless worried
about the severity of effects, the steepness of a dose response curve they had
produced and absence of a clear no observed adverse effect level (NOAEL) in the
rat developmental study. The officials found it necessary to apply an increase
safety factor in establishing the acceptable daily intake for consumers (ADI),
acute reference dose for consumers (ARfD), and admissible operator exposure
level (AOEL). Based on this data PSD set the following end-point values based on
the rat development study with a safety factor of 1,000 fold:
- A temporary ADI of 0.01 mg/kg, based on the minimal effect
of 10 mg/kg body weight per day
- An AOEL of 0.01 mg/kg bw/d
- An ARfD of 0.01 mg/kg bw/d
For many teratogenic compounds, adverse effects on foetal
development can be produced by a single exposure at a crucial period during
pregnancy. According to PSD, this was an important factor when considering those
working with products containing tridemorph.
Furthermore, the studies showed that
the AOEL was exceeded when exposures to operators, resulting from the use of
products containing tridemorph, were estimated. Although PSD said it was
possible to reduce these exeedances by imposing requirements for the use of
additional personal protective equipment (PPE), making changes to the maximum
application rates of products, and imposing a requirement to apply products only
via tractors in closed cabs; the possibility of single exposures resulting from
splashes and spillages during mixing and loading would still present a
significant risk to women of child bearing age. On this basis, the Agriculture
Minister specified the following requirements, following advice from PSD and the
- All approval holders should carry out an active information
campaign to alert users of the products to the fact that the use of
tridemorph by women of child bearing age may carry a risk of adverse
reproductive effects. This includes warnings on the labels of products.
- Closed transfer systems must be used when transferring
formulations containing tridemorph from the container to the spray tank.
- Application formulations containing tridemorph must be
restricted to vehicles where the operator is protected by a closed cab.
- For all formulations containing tridemorph, the maximum
individual dose must not exceed 375g active ingredient per hectare. Approval
for uses were revoked where the maximum individual dose exceeded this limit.
- The following additional PPE requirements were specified
for all formulations containing tridemorph:
Operators must wear suitable protective gloves when handling contaminated
- The packaging for all formulations containing tridemorph
was restricted to 'wide-neck' containers only.
Other reports of reproductive effects
In 1995 tridemorph was listed as teratogenic (a
substance that may cause birth defects) in Sax and Lewis Dangerous Properties of
Industrial Materials(12). It has also been identified as a potential endocrine
disruptor by Germany's Federal Environment Agency(13) because of concerns over
its effect on mammalian ovaries. In 1990 the US publication Pest Line reported:
"Embryoethality, cleft palate and other anomalies, and maternal toxicity
were reported in a study of pregnant rats and mice."(14)
In rats, following oral consumption,
tridemorph is rapidly absorbed, and is almost completely eliminated within two
days. Residues in cereal grains at harvest are <0.05 mg/kg. Its half-life in
soils has been measured at 20-50 days in laboratory tests, and 14-34 days in
It is not often detected in water
because of the lack of adequate analytical techniques. In the UK, the Working
Party on the Incidence of Pesticides in Water noted in 1996 that it was one of
the most significant widely used fungicides for which methodology was
Tridemorph is harmful to fish and/or
other aquatic life. Users are reminded not to contaminate surface waters or
ditches with the chemical or used container17.
The LC50 [the concentration required
to kill half a population of laboratory test animals] (96 hr) for trout is 3.4
For bees, the LD50 (24 hr) is
In the UK, MAFF requires that further data
(unspecified) from the approval holders to supplement the existing data package
(see also above Reproductive effects)(20).
There is little data about tridemorph in the public domain.
After years of use, PSD is only just about to publish an evaluation. The
substance will not be reviewed by the European Union under the Registration
Directive. The US EPA has no factsheet, nor has the US academic source Cornell
University, which publishes a number of factsheets on pesticides on the net. No
evaluation on toxicology or food residues has been published by Codex, the joint
UN FAO/WHO food standards agency and there are no MRLs for food. Notwithstanding
the lack of data, in the UK, tridemorph was the 18th most widely used active
ingredient (by area) on arable crops in 1996, and the 23rd by weight(21).
1. Tomlin, CDS, The Pesticide Manual, British Crop Protection Council,
3. R. Whitehead, The UK Pesticide Guide 1999,
4. Active substances in authorised Plant Protection Products, European
Commission, September 1995.
5. TE Lacher, SR Mortensen, KA Johnson and RJ Kendall, Environmental
aspects of pesticide use on banana plantations, Pesticide Outlook, 1997, Vol
6, No. 6:24-27.
6. Pers. comm. Pesticides Safety Directorate, an Executive Agency of
MAFF, 5 May 1999.
7. Pers. comm., Miles Thomas, Pesticide Usage Survey Group, MAFF, Central
Science Laboratory, May 1999.
8. WHO Classification of Pesticides by Hazard 1998-1999, International
Programme on Chemical Safety, WHO/PCS/98.21.
9. Op. cit. 3.
10. Pestline, Material Safety Data Sheets for Pesticides and Related
Chemicals, Vol II, Occupational Health Services Inc. 1991.
11. Op. cit 6.
12. Dangerous Properties of Industrial Materials", 7th Ed., by N.
Irving Sax and Richard J. Lewis. 1995.
13. ENDS Report 290, March 1999.
14. Op. cit. 10.
15. Op. cit. 1.
16. Pesticides in Water, Report of the Working Party on the Incidence of
Pesticides in Water, Department of the Environment, HMSO, London, 1996.
17. Op. cit. 3.
18. Op. cit. 1.
19. Op. cit. 1
20. Op. cit. 6.
21. Pesticide Usage Survey Report, No. 141: Arable Farm Crops in Britain
1996, MAFF, 1997.
[This article first
appeared in Pesticides News No.44, June 1999, p20-21]