Chinese scientists declare safe alternative to toxic paraquat weed killer - South China Morning Post

However, its high toxicity to humans has become a serious problem and has curbed its application.

07:58

Why is the Chinese government so concerned about food security?

Why is the Chinese government so concerned about food security?

Statistics show that in some areas of Asia, there is a 50-90 per cent mortality rate associated with the estimated 2,000 patients a year who suffer paraquat poisoning; worldwide, 20 deaths per million people result from paraquat poisoning because there is a lack of specific antidotes.

Using paraquat as a herbicide has been banned in more than 20 countries and regions. China stopped producing paraquat from July 1, 2014, and prohibited its sale and use two years later. However, related poisoning incidents and deaths still occur now and then – intentionally or unintentionally.

Some literature says extensive paraquat application leads to widespread residue on the soil surface and in aquatic environments and that it ultimately enters the food chain. Exposure to it has been found to increase the risk of developing idiopathic (from unknown causes) Parkinson's disease.

Peng Ai, the head nephrologist at Shanghai 10th People's Hospital, whose team is expert in treating paraquat poisoning, has thought about how to deliver a herbicide that is both effective and non-toxic.

His team, in collaboration with researchers led by Tang Wenjun at the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, and through experiments and screenings, discovered a new type of molecule called dienediamine that meets the requirements.

It is safe before being applied to weeds. But after spraying on weeds, the dienediamine molecule can convert to paraquat under natural sunlight and ambient air conditions, as a comparable herbicide.

The team said experiments on mice showed that this alternative did not damage vital organs such as the heart, liver, lungs, and kidneys. Their discovery was published in the peer-reviewed journal Molecular Plant this month.

Zhang Zhanhong, a scientist at the Hunan Academy of Agricultural Sciences who was not associated with the study, said the development of this new herbicide was "very meaningful" if it could be applied in real agricultural practice.

The researchers wrote: "Developing a non-toxic herbicide with comparable efficacy to paraquat will contribute to global food security and help prevent related fatalities".

China's genetically modified giant-rice harvest feeds into food-security drive

Agricultural challenges facing modern society include how to protect crops sustainably, eliminate diseases spread by pests, maintain or promote biodiversity and combat weeds.

The threat by invasive plants and weeds to agriculture is multifaceted, involving their competition with crops or other essential plants for survival space, sunlight, soil, water and nutrients. Weeds can also serve as hosts or carriers for plant pathogens and pests.

Besides choking soybeans, corn and wheat crops, some weeds are quickly evolving to resist some of the most advanced herbicides.

In the pursuit of global food security over the past seven decades, herbicides have played a significant role. They have also caused damage and raised concerns.

In China, the high cost of manual or mechanical weed control and governmental prohibition of burning them all contribute to the widespread use of herbicides.

However, despite having no impact on crops, "herbicides exhibit a long residual period and can cause damage to soil structure, leading to a decline in fertility, " Zhang said.

"The harm caused by herbicides far exceeds that of pesticides, fertilisers and plant growth hormones, yet it hasn't raised comparable awareness."

After using herbicides in a cornfield, for instance, vegetables planted immediately afterwards typically grow poorly and soil remediation products are needed to repair the field.

"It is time to create a global process to transition toward safer and healthier food and agricultural production," its authors said.

02:01

Thousands of ducks released to protect Thai rice fields from pests

Thousands of ducks released to protect Thai rice fields from pests

In April, the Hong Kong Consumer Council found that among all 27 samples of dried goji berries tested, pesticides that could pose health risks were found in 70 per cent of the samples, although at levels within local and European standards.

"The council urges the industry to reduce the use of pesticides and other chemical pest control methods to cut risks to humans and the environment," said Nora Tam Fung-yee, chairwoman of the council's research and testing committee.

It is not known when the new chemical developed by the Chinese scientists can be used by farmers. The Post has sought answers from the leading authors but is yet to receive a response.

China's skyscraping pig farms are high on the hog amid food-security drive

Technology is constantly transforming agricultural practices that date back to ancient times. For example, in 2022 scientists from institutions such as the Federal University of São Carlos in Brazil developed nanotechnology to encapsulate herbicides, reducing the use of a specific herbicide by 80 times.

Some go further, intending to change the game of weed control by using an entirely new mode of action to combat the out-of-control weed species.

In the United States, Professor Todd Gaines from the University of Colorado is partnering with the biotech company AUM LifeTech to research the application and methods of an emerging gene-silencing weed-control technology. Their two-year project was announced last year and funded by the Defence Advanced Research Projects Agency.

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