A SINGAPOREAN student has made it to the finals of the first Google Science Fair.

The global competition is for budding young scientists aged 13 to 18. Fifteen finalists will present their projects at Google's headquarters in the United States next month.

Shaun Lim, 18, said he was very lucky to be selected as one of the finalists. More than 7,500 people had submitted projects.

'If you think about it, the odds were less than 1 per cent,' said the final-year student in the six-year programme at Anglo-Chinese School (Independent).

The winner will get US$50,000 (S$62,000) and prizes from the competition's partner organisations. These include a trip with National Geographic and an internship at a research centre.

Shaun's project is a type of herbicide created from plants such as sunflowers and casuarinas. It can be used to replace current herbicides which contain chemicals harmful to people.

In 2009, scientists found that a popular herbicide called Roundup could lead to birth defects and cancers.

Chemicals created by plants, on the other hand, have been used in foodstuff such as coffee for decades.

The natural herbicide is made by pouring water over, for example, sunflowers. The water absorbs chemicals called allelochemicals produced by the sunflower leaves.

The collected water can then be used as herbicides against weeds such as wild oats, which affect barley plantations.

Other natural herbicides such as oil extracts from black walnut trees have been created by scientists over the last decade.

But their use has been limited as the chemicals attack only certain plants, whereas artificial herbicides have a wider range of targets.

Shaun said the trend could change if more harmful side-effects of commercial herbicides are uncovered.

'The natural herbicides are more friendly on the environment and people.'

He added that an effect of climate change has been to make the plants more efficient weed killers.

His experiments show that ultraviolet light in sunlight makes the plants produce more of the allelochemicals.

'If the ozone layer continues to get thinner and thinner, more ultraviolet light will get through and more chemicals will be produced,' he said.

He intends to continue the research in university. He said chemicals in the plants may have other uses, for example, in the medical industry.

Research has shown that chemicals called hemicelluloses in sunflowers can be used to prevent gastric cancer in mice. Studies on human beings are ongoing.

The project was started as part of Shaun's curriculum in his school.

Representatives from Google declined to comment on the project as the judges are still evaluating the finalists.

The panel of judges includes Nobel prize winners, university professors and science magazine editors.

zengkun@sph.com.sg