A Complete Risk Assessment
Greetings from Meindert de Jong
vlinders at rcl.wau.nl
Fri Jan 24 21:02:53 EST 1992
Dear List-Owners of COMPBIO-l:
Herewith an article on a biological risk analysis.
It emphasizes the risk evaluation by the national public and
the international scienctific community. It illustrates my
individual opinion rather than much scientific details.
Hope it is suitable for this list!
OK here goes......................
Subject: A Complete Risk Assessment for Biological Contro
The present study is, as far as I know, the first (published)
quantitative risk study in plant pathology. It is a Dutch case
study in biological control of Black cherry (Prunus serotina),
an introduced forest pest, with help of the 'Silverleaf fun-
gus', a wide spread wood invader.
Black cherry can be controlled by treating its stumps with the
Silverleaf fungus. The Silverleaf fungus is pathogenic to
Black cherry but also to cultivated plum and cherry. After
controlling, airborne spore might reach an infect fruit trees
outside the forest. This was identified as being risky. Before
developing the biological control method, it was necessary to
assess the hazard posed by an artificially increased populati-
on of the fungus to fruit trees.
Accordingly, a risk analysis was performed, consisting of
field work, and computer simulations. Risk to fruit trees
outside a forest with the intended biological control was
modelled. The spore flight outside the forest was quantified
with help of the Gaussian plume model, commonly used in air
_____Absolute and Relative Risk_____
A short-term version of the Gaussian plume model was used to
calculate the 'absolute risk' as the aerial spore concentrati-
on outside the forest due to biological control. It was con-
cluded that risk to fruit trees was appreciable at 500 m
distance and negligible at 5000 m distance.
The 'relative risk' was calculated as the ratio of added spore
concentration, due to biological control, over natural spore
concentration, due to normal presence of the fungus in nature.
A long-term version of the Gaussian plume model was used for
this purpose. (Billions of computations were performed.) It
was concluded that the added risk was about equal to the
_____Judgement by the State Authority_____
This technical study could estimate risk to fruit trees. It
could not, however, answer the question which level of absolu-
te or relative risk is acceptable to fruit growers. A Dutch
State Authority charged with the judgement on the safety of
biological control using the Silverleaf fungus has now offici-
ally permitted the biological control of Black cherry, provi-
ded that the distance between a forest with biological control
and fruit growing areas is at least 500 m. It has accepted our
conclusion that added risk is comparable to or less than
_____Acception by Society at large_____
The hazard of deploying the fungus for control of Black cherry
throughout The Netherlands was estBimated by registering the
simultaneous occurrence of forests with Black cherry and
fruit-growing areas in grid cells on a map of the country. (It
was a computer drawn figure but nobody knew that.) Hour squa-
res with both Black cherry and fruit production were rare. It
was this picture, published by several newspapers and magazi-
nes, that might have had a great impact on risk acceptance by
the Dutch society at large.
A Thesis was written in the Dutch language mainly, and some
papers for the international scientific community. For instan-
ce, one manuscript of a paper was sent to an American Journal.
The reviewers gave a mixture of opininions. However, the edi-
tors suggested to transform the manuscript into a feature
article. Feature articles in this Journal are intended for
international audiences and also are used by teachers and
professionals outside the disciplin of plant pathology.
I received many requests for reprints from the university
community, a few bioscience labs, and even one from an oil
compagnie. Some Canadian researchers contacted me because the
Silverleaf fungus plays an important role in birch decline of
North American forests. Other Canadians would apply the sil-
verleaf fungus for some of their native woody weeds.
An USA University Professor stated: "Your study illustrates to
scientists and regulators here that risk analysis can be done
scientifically and that restrictions can be made on demonstra-
ted not conjectural risk".
The risk analysis was cited in a study of risks to nature
caused by introduction of genetical engineered plants.
The present risk analysis, providing a fairly objective rela-
tive risk measure, paved the way for the approval of biocon-
trol in the sense of "yes, if the various political concerns
can be satisfied". A Dutch commercial company has shown an
interest in producing the biological herbicide. A biocontrol
agent based on this fungus will be on sale soon.
If you want to have any documentation, or if you should appre-
ciate my assistance in your research, *please feel free* to e-
mail me, or to write me at: Tarthorst 195, 6708 HJ Wageningen, NL
dr Meindert D. de Jong
e-mail: Vlinders at rcl.wau.NL
phone: (+31) 8370 21937
photo: de Jong et al.'90. Risk Analysis for Biological Control.
A Dutch case study ... Plant Disease 74: 189-194.
e-available: de Jong et al.'91. Modelling the spore escape ....
from a larch forest ... Neth.J.Pl.Path.97: 55-61.
Domain: curtiss at umiacs.umd.edu Phillip Curtiss
UUCP: uunet!mimsy!curtiss UMIACS - Univ. of Maryland
Phone: +1-301-405-6710 College Park, Md 20742
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