OSOYOOS TIMES-May 26, 2010

By Paul Everest – Osoyoos Times

A study published this month that looked at the effects of a trio of pesticides on the early-life stages of great basin spadefoot toads and Pacific treefrogs living in Osoyoos found that pesticide levels observed in this area caused death and deformities to the amphibians, even though the levels “met the requirements for federal water quality guidelines.”
The study, entitled “Effects of Environmentally Relevant Concentrations of Endosulfan, Azinphosmethyl, and Diazinon on Great Basin Spadefoot (Spea Intermontana) and Pacific Treefrog (Pseudacris Regilla)” was conducted from 2004 to 2008 and was published in the American Journal of Environmental Toxicology and Chemistry.
It used amphibian eggs from several different locations in the Osoyoos-Oliver area in a series of experiments in the field and in laboratories.
Great basin spadefoot toads are on British Columbia’s Blue List and are considered vulnerable to human actions.
According to the B.C. Environment Ministry, Pacific treefrogs are “quite abundant in B.C. and can use a variety of habitats, so it is not considered to be of conservation concern.”
The laboratory part of the study was carried out in two phases where eggs and tadpoles were subjected to the same concentrations of pesticides found in water samples in this area.
The water samples collected revealed that the three pesticides the study focused on “were among the highest concentrations in ponds that experienced substantial embryonic mortalities,” the study found.
In the first phase of the study, 10 embryos were exposed to pesticides for eight days and “significant mortality” was observed when the spadefoot toad embryos hatched after being subjected to the “highest lethal concentrations” of endosulfan.
Alexandra de Jong Westman, a biologist with Vernon-based Summit Environmental Consultants Ltd. and one of the authors of the study, said that according to federal guidelines, the “highest lethal concentration” refers to the amount of pesticide required to kill 50 per cent of a test population over four days.
Referred to as an LC50 test, the lethal concentration of endosulfan for amphibians is roughly 7.7 milligrams per litre.
In the second phase in the laboratory, tadpoles were exposed to the same pesticides for eight days.
According to the study, “Endosulfan induced significant effects on behavior and morphology of (Pacific treefrog tadpoles) and significantly reduced survivorship of (great basin spadefoot toad tadpoles)” when the pesticide was introduced at a concentration of 0.06 milligrams per litre of water.
“Abnormal behavior and excitability was observed in both species, with (Pacific treefrog) tadpoles being more sensitive,” the study states. “At (0.06 milligrams per litre) of endosulfan, (Pacific treefrog tadpoles) also lost pigmentation and exhibited abnormal tail morphology.”
It was determined that while the embryos and tadpoles might be resistant to one of the pesticides used in the study at concentrations “typically found in the Okanagan Valley,” a combination of pesticides, or the “additive effect” was much more toxic.
“Additively, however, the toxicity for these three chemicals to spadefoot eggs may be up to 40 per cent, suggesting that exposure in the wild to a higher number of pesticides with varying mechanisms of action would cause a higher rate of mortality.”
The study also found that, in addition to experiments with the pesticides in the laboratory, field experiments with “similarly aged embryos and tadpoles” turned up mortality rates exceeding 80 per cent in some sprayed orchards.
“While there were up to 17 pesticides detected in the ponds where the eggs were exposed, the estimated additive effect of only three chemicals tested in the present study was, on average, 40.5 per cent (mortality rate) for (Great Basin spadefoot toads) and 14 per cent for (Pacific tree frogs).”
According to the study, the pesticides used in the experiments are “currently being sold by South Valley Sales to orchardists in the South Okanagan valley.”
Endosulfan, which also goes by the commercial name Thiodan, is a pesticide used to protect vegetables, fruits, timber and several other crops.
It can still be used in Canada, but Health Canada has ordered that the product is “not to be used in and around homes or other residential areas such as parks, school grounds and playing fields. It is not for use by homeowners or other uncertified users.”
Health Canada also made it necessary to include warnings for endosulfan stating that it is toxic to aquatic organisms, birds, small wild mammals, bees and other beneficial insects.
Azinophosmethyl, which also goes by the commercial name Guthion, is a pesticide sprayed on crops such as apples, pears, cherries and peaches.
While the U.S. Environmental Protection Agency has banned many of its former uses and is currently phasing out its remaining uses, it is still legal to use azinophosmethyl in Canada.
According to Health Canada, diazinon is an insecticide used “on a wide variety of greenhouse food crops, terrestrial feed crops, terrestrial food crops, outdoor ornamental and nursery crops, livestock, non-crop land and on seeds as a protective seed treatment.”
Last November, after conducting a “re-evaluation” of diazinon, Health Canada granted “continued registration of some diazinon uses while requiring a phase-out of other uses of diazinon products for sale and use in Canada.”
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