`The Canaries in the coalmine'

This article is the first in an occasional series on the dangers of pesticides to the environment which will be contributed by members of the Pesticides Focus Group.


This article is the first in an occasional series on the dangers of pesticides to the environment which will be contributed by members of the Pesticides Focus Group.

This group, formed last November, is composed of ten people from varying backgrounds including research, horticulture, conservation, pest control, golf course management and Government.

The mission statement of the committee is "to promote the safe and responsible use of pesticides, and actively encourage the use of alternatives, through the implementation of new policies, regulations and educational programmes''.

The focus group has a number of objectives. One includes providing Government with suggestions on issues concerning the importation, sale and use of pesticides.

Another objective is to promote the training and licensing of all major users of pesticides. And, as stated in the mission statement, a third objective of the focus group is education.

To that end, it is hoping that the following series of articles will help raise public awareness about pesticides and explain why it feels it is time to bring pesticide usage in Bermuda into the spotlight.

By Jamie P. Bacon, PH.D Bermuda Zoological Society Research Associate and Pesticides Focus Group Chairperson During the past decade, scientists have become increasingly concerned about the numbers of die-offs and deformities that have been observed in amphibian populations around the world.

Not only are they concerned for the future of these unique animals, but they fear what the deaths and deformities may signify about the health of the environment as a whole.

Amphibians, which include frogs, toads, salamanders and newts, have thin, permeable skins and shell-less eggs that are protected only by a jelly like covering. Thus, these animals are more sensitive to environmental contaminants than reptiles, birds and mammals.

Because of their vulnerability, researchers feel that amphibians are likely to show the effects of environmental problems before many other groups of organisms.

For this reason, amphibians have frequently been dubbed "the canaries in the global coal mine''. Like the canaries, whose death warned coal miners that toxic gases were present, amphibian deaths and deformities might be a warning that their habitats, and ours, are becoming poisonous.

Bermuda's frogs and toads have not been exempt from what's been happening to amphibians in other countries. Bermuda has no native amphibians, but two species of whistling frogs and one species of toad were introduced in Bermuda between 1880 and 1900. All three species became well established and seemed to thrive.

There are signs that Bermuda is no longer an Island paradise for its adopted amphibians however. One species of whistling frog apparently has disappeared since 1994 and there is evidence that the number of giant (aka marine or cane) toads in many areas has declined as well.

Perhaps even more disturbing is the high incidence of deformities that has been observed in Bermuda's toads and toadlets (newly transformed toads) during the past two years. Nineteen percent of the 726 adults examined from eight parishes had some type of deformity.

Furthermore, the deformity rates of toadlets at particular breeding sites was as high as 47 percent. This far exceeds a normal background deformity rate of two percent or less.

Although many of the deformities were minor, such as shortened or missing toes, others were quite significant including missing or misplaced eyes and missing limbs or feet.

And I can tell you from experience that few things are as disconcerting as a toadlet staring at you from an eye growing on its back! One explanation for the deformities seen in North American amphibians is that chemicals such as pesticides and fertilisers are disrupting the normal development of these animals.

While researching whether chemicals might also be responsible for the toad deformities seen in Bermuda, it became clear to me that pesticides, a specialised group of chemicals, can pose a variety of threats to amphibians. A pesticide by its very nature must kill or neutralise its target species.

Pesticides include herbicides, insecticides and fungicides as well as chemicals that might be used to kill other pests such as rats and birds.

Unfortunately, in many cases, pesticides also kill non-target species such as amphibians. An example of this occurs with Roundup, a very popular herbicide in Bermuda and elsewhere which has been used to control water weeds in some countries.

Because of its toxicity to frogs and tadpoles, the Australian government has banned the use of Roundup (and 73 other herbicides) near water. It turns out that it is not the active ingredient (glyphosate) that does the killing, but the surfactants (wetting agents) contained within the formulation of the pesticide.

And this highlights one of the problems with trying to determine the toxicity of any pesticide. Frequently, only the active ingredients are tested in toxicity studies, not the breakdown products or "inert'' ingredients.

Only after suspicions are aroused do the hazardous nature of these other compounds come to light.

Probably just as important as the lethality of many pesticides is the array of non-lethal effects that they can produce.

For example, exposure to a number of pesticide active ingredients (AIs) such as the herbicide diuron, the fungicide mancozeb or the insecticide endosulfan can slow growth in tadpoles.

For some species, the resulting delay in metamorphosis may mean that a habitat could dry up before the tadpoles have a chance to transform into little toadlets or froglets.

Or, it could mean that they mature later and are `out of synch' with the availability of a particular food source.

Research has also shown that smaller toadlets and froglets become less fit adults.

And there is evidence that when animals metamorphose at a smaller than normal size, their immune systems may be seriously compromised.

Which brings up another known effect of pesticides, immune system suppression.

It has been suspected that a reason behind some of the die-offs witnessed in various amphibian species is that chemicals such as pesticides have weakened the immune systems of these animals.

This increases their susceptibility to diseases.

Unfortunately, Bermuda's amphibians appear to be copying their cousins overseas as evidence of immune systems suppression has been found in some Bermuda whistling frog and toad specimens.

If the incidence of immune system suppression is widespread here, then the accidental introduction of an amphibian disease organism could trigger a major die-off.

Another effect that exposure to pesticides such as Ambush (AI permethrin) and Sevin (AI carbaryl) can have on tadpoles is that their feeding and predator avoidance behaviour is altered.

After being exposed to tiny amounts of Ambush for 22 hours, for example, tadpoles did not dart away when prodded as they normally would.

Instead, they twisted about in a jerky, disorganised manner which certainly wouldn't have prevented their being snatched up by a predator.

Such abnormal behaviour could last for over a week.

An even more insidious effect of certain pesticides is their ability to sabotage reproduction.

For example, out of a group of embryos exposed to minute amounts of mancozeb, 60 percent of them became males, and 40 percent developed no identifiable ovaries or testes.

Other studies showed that exposure to a breakdown product of mancozeb could produce 100 percent males in one frog species and 100 percent females in another.

Such an event could have dire consequences since a population composed of all males or all females isn't going have offspring.

Although the various effects of pesticides described above show ways that our amphibians, especially our toads which breed in water, can be affected by pesticides, the initial question still remains to be answered.

Could pesticides be causing the deformities seen in our toads and toadlets? The answer, simply, is yes.

Laboratory studies have shown that at least two fungicides used in quantity here, Manex (AI maneb) and Dithane (AI mancozeb) can cause skeletal deformities in frogs.

Eye deformities have been produced with permethrin and mancozeb as well.

This does not necessarily mean that pesticides are causing the deformities seen in our toads.

All we can say at this point is that they could be, and more research is being done to try to see if this is the case.

But, the fact that they could be causing deformities as well as the other effects described above suggests that we need to use pesticides with caution.

And, we need to try to use safe alternatives whenever possible.

This is not just for the sake of our toads and whistling frogs, but for our sakes as well.

Many pesticides, including some used in quantity here, are known to be hazardous to humans.

Not only are many them carcinogenic, but they can cause birth defects, thyroid and other endocrine problems, asthma, neurological disorders and immune system deficiencies.

Since pesticides are being sprayed or applied near our homes and on our produce, even the possibility that they are accumulating to levels that are toxic to amphibians warrants our attention.

Thus, we may be wise to interpret the woes of Bermuda's amphibians as a warning; they may be telling us something important about our environment. And they may not be the only ones.

Last summer young sparrows with twisted, deformed limbs were found near the south shore in Devonshire.

As it may be difficult to pinpoint what is causing the deformities in toads and sparrows, we feel that it is time to use the precautionary principle.

On an Island of only 20 square miles, it is much better to be safe than sorry with pesticides, or any other hazardous substances for the matter.

Dr. Jamie Bacon

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