08 May 2012

NEA replies to spraying of chemicals on Chek Jawa

I've received NEA's reply today, in response to the my email to them about a pair of NEA officers spraying chemicals to control mosquitoes at Chek Jawa. Thanks to everyone who left polite and constructive comments on that earlier post.
NEA clarifies that they "do not use any chemicals at Chek Jawa" but because "the population of Anopheles mosquitoes on Pulau Ubin makes it a malaria receptive area", NEA is applying Bti and "if necessary, anti-malaria oil" that "does not contain any pesticides and is bio-degradable".

Here's the full correspondence chain.

NEA's reply, forwarded to me by NParks on 8 May 2012

We refer to your query below. We share the writer’s concerns on the use of chemicals at Chek Jawa for mosquito control and would like to clarify that NEA does not use any chemicals at Chek Jawa.

The population of Anopheles mosquitoes on Pulau Ubin makes it a malaria receptive area. Anopheles mosquitoes are the principal vectors of malaria. Due to the large number of visitors including tourists from malaria endemic countries and residents to the island, it is imperative that adequate control measures are put in place to prevent a localised malaria outbreak.

For such ecologically sensitive areas, NEA prescribes the use of environmental manipulation and biological control tool wherever possible. For environmental manipulation, drains were built to drain away stagnation of water and breeding habitats remove. For biological control, Bacillus thuringiensis serovar israelensis (Bti) is used. Bti based products have been widely tested and used worldwide in mosquito control projects. Bti will only kill mosquito larvae specifically and a few flies species such as chironomids and blackflies. The United States Environmental Protection Agency (USEPA) categorizes the risk posed by Bti strains to non-target organisms as minimal to non-existent. Scientific evidences indicate that Bti is non-infectious and non-toxic to humans and other mammals. The Bti that has been approved for use by NEA meet the World Health Organisation Pesticides Evaluation Scheme specifications and guidelines for use and is also approved for use in drinking water.

If necessary, anti-malaria oil will be applied to pools of stagnant brackish water when profuse mosquito breeding has been found. The oil does not contain any pesticides and is bio-degradable. The oil cuts off the oxygen to the mosquito larvae and pupae killing them in the process.

The above is a response to my email to NEA and NParks sent on 16 Apr 2012

Dear all, On Saturday, 14 Apr 2012 at around 9.15am, I saw two NEA officers dilligently spraying mosquito control chemicals directly onto the natural ecosystems of Chek Jawa. I observed them doing so all along the mangrove boardwalk, spraying the back mangroves from all sides. They then got off the Coastal Boardwalk and sprayed the rocky shore including areas that would eventually be innundated at the high spring tide. The NEA officers were friendly and professional, and I was glad to see that they even removed some litter that then came across while doing their work.

I overheard that there were plans to fog the area as well. From talking to researchers who visit Chek Jawa, I understand spraying in the mangroves and rocky shores has been going on regularly, as often as every two weeks. One researcher said it has happened since 2008.

I believe this action was probably taken because of complaints by visitors of mosquitoes? I do understand that park managers often have to balance such complaints with the need to protect biodiversity.

Indeed, the mosquitoes at Chek Jawa can be abundant and fierce especially in the back mangroves. When I guide with the volunteers of the Naked Hermit Crabs, we have not had visitor complaints about mosquitoes. We alert our visitors to be prepared with repellent, and we ourselves dress in longs to minimise bites.

In fact, the most mosquito infested area, which I call "Mosquito Valley", has some of the best variety of marine life that even young children can easily view from the boardwalk. It is among our favourite stretches with much marine life. The kids have a great time there despite the mosquitoes. And the rocky shore and area adjacent is full of life too.

I understand from NParks officers managing Chek Jawa that NEA is only supposed to conduct mosquito control on areas not affected by the tides.

But even in areas above the tidal influence, wildlife such as wild boar may drink the freshwater. Currently, there is a friendly mother wild boar with her seven piglets and two older offspring hanging around Chek Jawa most of the time.

Most people come to Chek Jawa to see wildlife and nature, not just large animals but also small fishes and invertebrates like crabs. If mosquito control reduces such sightings, it will affect the experience of these visitors. Visitors may then also think there is 'nothing' to see at Chek Jawa and thus reduce support for conservation of Chek Jawa in the long term.

I feel spraying and fogging is not an ideal response to complaints about mosquitoes at Chek Jawa. Other responses should be considered.

I have posted about this incident with lots of photos of the NEA officers at work. Many people have left polite and constructive comments on this blog post.

I hope NParks and NEA can put an immediate stop to spraying and fogging at Chek Jawa and other areas with important and rich biodiversity at Pulau Ubin. And consider some of the suggestions shared in this public feedback.

Thank you.

Ria Tan

A summary of our questions, information, comments and suggestions posted on the wild shores of singapore blog post.


What chemicals are used in the spray?

Has research been done on the impact of these chemicals especially on non-targetted organisms?


Not all families with young children are put off by mosquitoes, as The Heng Family indicated in their comment.

If chemicals used in the spray kill all invertebrates, these may cause an imbalance in the ecosystem that will eliminate natural predators of the mosquitoes (such as dragonflies). Spraying can thus potentially make the mosquito problem worse.

In addition, killing non-targetted organisms will disrupt the food chain both in the sea and on land resulting in a widespread impact that will affect biodiversity well beyond the spray zone.

Some suggestions as an alternative to spraying and fogging chemicals:

Think of ways to increase the population of the natural predators of these mosquitoes.

Alert visitors to expect mosquitoes in certain stretches of the boardwalk (e.g., a sign at the entrance to the Mangrove Boardwalk and at the Information Kiosk, post this information to the website.)

Sell repellent at the Information Kiosk.

Use this as an opportunity to educate the public about a natural ecosystem and how mosquitoes are part of nature. How mosquitoes are eaten by natural predators. Why spraying chemicals will result in an imbalance. And how visitors can protect against bites by the simple use of repellents or wearing appropriate clothing.

Robert Teo of Ubin NParks replied on the same day

Thanks for the feedback.

We’ve checked with NEA. They were carrying out routine spraying of Bti (Bacillus thuringiensis israelensis), a bacterium that is used widely as a biological control agent against mosquito larvae. This is an environmentally friendly alternative to spraying of mosquito oil to control disease mosquitoes as it does not affect non-target species.

To which I replied on the same day

Thanks Robert for this information.

I have a few more questions about this.

Does this mean that this treatment will continue on Chek Jawa regularly?

Will they continue to spray the back mangroves?

And continue to spray the rocky shore?

The substance they sprayed had a strong kerosene-like smell. Is this what Bti should smell like?

I did a brief google search on Bti and found some information which might be of interest to you

From the Washington State Department of Health

Bti is only effective against actively feeding larvae, and does not affect mosquito pupae or adults.

The Department of Ecology does not recommend application to most wetlands because natural predators in the ecosystem can control mosquito larvae.

Some studies suggest that continuous application of Bti over a period of 2-3 years to wetlands may result in an overall decrease of biodiversity (from Siegel, JP and JA Shadduck, 1990. Mammalian Safety of Bacillus thuringiensis israelensis in Bacterial Control of Mosquitoes and Black Flies: Biochemistry, Genetics and Applications of Bacillus thuringiensis israelensis and Bacillus sphaericus, pp 202-217. Editors: Barjac and Sutherland. New Brunswick: Rutgers University Press.)

from Long Lasting Persistence of Bacillus thuringiensis Subsp. israelensis (Bti) in Mosquito Natural Habitats

The common belief that commercial Bti is easily cleared from the ecosystem has not yet been clearly established. Our results raise the issue of the persistence, potential proliferation and environmental accumulation of human-spread Bti in natural mosquito habitats. Such Bti environmental persistence may lengthen the exposure time of insects to this bio-insecticide, thereby increasing the risk of resistance acquisition in target insects, and of a negative impact on non-target insects.

Thanks for looking into this.

NEA finally responded today (8 May 2012) after Ubin NParks sent them a couple of reminders.

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