Broad-spectrum insecticides in Japan

| 26th May 2020
Rice Terrace at Kamogawa, Chiba, Japan
Tsuyoshi Matsumoto.
Two insecticide types - in addition to neonicotinoids - continue to pose a threat to aquatic life in Japan.

The goal must become instead the complete elimination of such chemicals.

Chemical companies are taking advantage of Japan’s weak laws on pesticide use by selling a wide variety of broad-spectrum pesticides for use in rice farming, including neonicotinoids banned in other countries.

But other pesticide types with similarly devastating effects on aquatic ecosystems continue to be sold and promoted, such as Trebon, a synthetic pyrethroid sold by Mitsui Chemicals, and Prince, containing fipronil, a phenylpyrazole sold by BASF. 

Simultaneously, a worldwide insect extinction event is ongoing in which broad-spectrum insecticides are implicated as a leading cause.


Japanese rice fields are losing aquatic insects such as iconic autumn darter dragonflies that use the flooded fields in the nymph part of their lifecycle. The resulting pollution of rivers and lakes has also led to the collapse of the fishery in Lake Shinji in Shimane Prefecture, which scientists have connected to neonicotinoid use in surrounding rice fields.

The process of removing dangerous pesticides from use is an arduous one, with companies like Bayer fighting bitterly to continue sales of each product both in court and with campaigns to discredit any critical scientific studies. In recent years, this scorched-earth approach has led to environmental groups focusing their energies on neonicotinoids, eventually achieving bans on some products in the European Union. 

According to information provided by Japanese NGO Act Beyond Trust, five main companies, Bayer, BASF and Syngenta from Europe and Sumitomo Chemical and Mitsui Chemicals from Japan, manufacture and sell rice-field insecticides in Japan. With negative publicity surrounding neonicotinoids, Mitsui Chemicals is switching its sales campaign to a different class of insecticide while continuing to quietly sell dinotefuran, its flagship neonicotinoid. 

The goal must become instead the complete elimination of such chemicals.

Mitsui Chemicals promoted dinotefuran as a featured product in its Corporate Social Responsibility (CSR) report for the year to 31 March 2018, stating that agriculture was expanding “due to growing demand amid a rising global population and economic development in emerging countries”.

Due to this, “regarding the insecticide dinotefuran and other active ingredients,” the company is “tapping the expertise of its partners to develop agrochemicals, expand the number of countries where these products are registered, and accelerate the pace of market release.”


However, Mitsui Chemicals was hedging its bets as neonicotinoids came into the spotlight for the role they played in disappearing bee populations, leading to dinotefuran being banned by France. In its 2018 and 2019 reports on  Environmental, Social and Governance (ESG), dinotefuran was not mentioned.

Replacing it for promotion as a flagship product was an insecticide of a different class. Marketed as “Trebon”, it is also a broad-spectrum systemic pesticide of a type known as synthetic pyrethroids. Commonly used in rice farming, these chemicals were also shown by studies over many years to be particularly hazardous to aquatic ecosystems. 

One study published in Environmental Toxicology and Chemistry in 1989 said that synthetic pyrethroids are “exceptionally active against many insects” and also “extremely toxic to certain aquatic and marine groups, including fish”. The chemical used in Trebon is etofenprox, which a review carried out by Mitsui Chemicals itself in 1996 for registration in America showed to be “very toxic to rainbow trout”.

Writing in Pest Management Science in 2009, Gary Barbee and Michael Stout went so far as to suggest replacing synthetic pyrethroids with neonicotinoids including Mitsui Chemicals' dinotefuran. They said that neonicotinoids are actually two to three times less toxic to crayfish.

Mitsui Chemicals’ Corporate Communications Division did not respond to a request for comments sent by fax and through their web site. However, in its ESG report for 2019 its justification in promoting Trebon is given as “responding to the food problem” and “contributing to stable and enhanced crop production”.


Interestingly, Mitsui promotes two classes of products, so-called “Blue Value” products which have “environmental contribution value” and “Rose Value” products which have “quality of life improvement contribution” value.

Trebon pesticide is promoted as a “Rose Value” product for the reason that it “addresses food problems". By not giving it a classification for its environmental contribution value, Mitsui Chemicals’ seems to be implicitly recognizing its hazardous nature. However, in the light of numerous studies the statement on Mitsui Chemicals’ website about Trebon that it is “safe for animals” is false. On the contrary, it is deadly to both vertebrate and invertebrate aquatic animals.

In fact, the extreme threat to aquatic ecosystems posed by this class of chemicals has been recognized for nearly 50 years. Writing in 1971 in the Bulletin of the World Health Organization, T. Narahashi described synthetic pyrethroids as “potent neuropoisons” and explained that for insects, the “symptoms of poisoning act primarily on the neuromuscular system”. In addition, Narahashi examined the poison’s deadly effects on the nerves of crayfish and squid.

Given that its hazardous nature has been established over so many years, it is hard to understand why Mitsui Chemicals is promoting Trebon as a featured product in its ESG reports. In addition to Japan, the product is promoted for rice farming in India and other countries, with biochemical company Biostadt India Ltd. claiming on its website that Trebon is effective on a “wide variety of insect pests” while simultaneously being safe for the environment as a “quality product from Japan thanks to its low toxicity attributes and low dosage application requirement”.

No mention is made of the deadly wider effects from synthetic pyrethroids reported by scientists over the years.


Another rice-field chemical that has been shown to menace aquatic ecosystems is fipronil, sold in Japan as “Prince” by German multinational BASF. This is also not a neonicotinoid, but of a different type known as phenylpyrazoles.

Similar to the other two classes of pesticides, fipronil is also a broad-spectrum nerve agent that acts on the nervous systems of insects. Now banned in China due to its devastating effects on rice-field aquatic insects, it continues to be sold in Japan although use in some areas may be decreasing.

Fipronil has been implicated in the widespread disappearance of iconic autumn darter red dragonflies across Japan. Dr. Ryo Futahashi, a dragonfly expert of Japan’s National Institute of Advanced Industrial Science and Technology, said by email: “In Toyama Prefecture, there is a correlation between the sharp decline of red dragonflies and the use of fipronil, and the improvement since 2010 is probably due to the decline in fipronil use since 2010.”

Sumiko Kobayashi of BASF Japan’s Corporate Affairs Division said by email: “BASF is committed to only offering products which help farmers grow more nutritious, high-quality food – while ensuring the protection of human and animal health and the environment.

"Fipronil has passed all toxicity tests required for pesticide registration by the Ministries of Agriculture, Forestry and Fisheries (MAFF) of Japan. Many other countries like the U.S., Canada, Australia, Brazil, Taiwan and Korea have also continued to permit the use of fipronil based on their science-based risk assessment evaluations of its safety when used as directed.”


However, a fact sheet on fipronil published by the National Pesticide Information Center in America states that “fipronil is highly to very highly toxic to marine and freshwater fish” and “highly toxic to freshwater invertebrates”. 

In Lake Shinji in Shimane Prefecture, the once-thriving fishery collapsed and a study by a team led by aquatic science expert Dr. Masumi Yamamuro of Tokyo University connected this to the use of neonicotinoids in surrounding rice fields.

However, they did not investigate what types of neonicotinoids are used in the region, or whether these two chemicals sold by BASF and Mitsui Chemical were mixed into the witch’s brew of insecticides that led to the death of the fish. 

In this situation, where multinational companies like BASF and Mitsui Chemicals are putting the full force of their sales departments into marketing these dangerous chemicals, it is hard to take seriously the claim that they practice corporate social responsibility or environmental sustainability.

On the contrary, they promote as featured products pesticides that have been unequivocally shown to be destructive to aquatic ecosystems. 


The efforts by environment groups to target individual broad-spectrum pesticides have become a game of whack-a-mole where chemical companies always have another product to feature with spurious claims of environmental safety.  

The goal must become instead the complete elimination of such chemicals, which by definition kill a wide range of the insects upon which both the ecosystem and other types of food production like honey production and fisheries depend.

This means rejecting the narrative from chemical companies with a vested interest in profiting from the sale of ecologically devastating broad-spectrum insecticides, that their type of intensive farming is the only way to feed the world.

If instead, a full-scale effort were made to rediscover and improve traditional farming methods that do not destroy a wide diversity of insect life and fisheries, might not a new agricultural revolution be possible that provides food security that is sustainable into the future?

This Author 

Phil Carter is a freelance environmental journalist based in Japan.

Image: Rice Terrace at Kamogawa, Chiba, Japan. Tsuyoshi Matsumoto.

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