By Quentin Sommerville Shanghai Correspondent, BBC News

There has been a lot of mudslinging between Washington and Beijing.

Henry Paulson is on a four day visit to China

Is China cheating at the game of global capitalism, as Washington suspects?

Or is the United States, worried that it will eventually be overtaken as the world's largest economy, trying to hold back a resurgent China, as many in Beijing believe?

US Treasury Secretary Henry Paulson's strategic economic dialogue was supposed to clean things up a bit and raise the level of debate between China and the United States.

The thinking goes that if the two governments talk, with cabinet level ministers from both sides meeting regularly, then it will foster greater understanding.

Eight months on, and the relationship is more toxic than ever.

Many are wondering if Mr Paulson's regular meetings with China's leadership are achieving anything.

His four-day visit begins in Qinghai in the west, where he'll be focusing on environmental issues, later he'll meet with President Hu Jintao and Vice Premier Wu Yi.

Undervalued yuan

The US Congress is still angry about what is sees as the deliberate undervaluation of the yuan by the Chinese government.

The US argument is that this makes Chinese goods artificially cheap and more attractive to consumers than US goods - and it's costing American jobs.

China says its goods are cheaper because its costs, such as wages, are lower.

Many in Beijing claim that if the yuan was revalued by the 20 to 40% that many congressmen would like to see, it would have catastrophic effects for China domestically, without resolving the trade deficit between the two countries.

But the US Senate's finance committee is not buying Beijing's argument and last week published a bill that would penalise Chinese goods with extra taxes if the yuan doesn't increase in value more quickly.

Poisoning pets

Poisoning thousands of American cats and dogs was never going to win China many friends in the US.

Some brands of Chinese toothpaste were involved in the safety scandals

Toxic Chinese-made dog food was the beginning of a long line of food safety scandals, that included the discovery of toxic seafood and toothpaste that contained anti-freeze.

"Made in China" was beginning to leave a bad taste in consumers' mouths.

Worse even than sick pets was the revelation that children's toys sold in America, but made in China, contained harmful amounts of toxic chemicals.

Unsurprisingly, US politicians and consumers were left questioning the safety of Chinese products.

However, given the importance of exports, the Chinese government moved with uncharacteristic speed to address worries about the "Made in China" brand.

Prime Minister Wen Jiabao, only last week, called for greater supervision and quality control and introduced new regulations.

Here in China there is a lingering suspicion that the US has made more of China's quality control issues than other countries in order to serve its protectionist instincts.

Focus on environment

Mr Paulson's first stop will be Qinghai, far from China's capitals of money and power, Shanghai and Beijing.

He has travelled far west to emphasise that environmental cooperation is somewhere the two countries might make progress.

The lakes in the region are shrinking and glaciers are melting.

China and the United States will need to work together if the world is to successfully tackle climate change.

America is the world's largest consumer of oil and biggest emitter of greenhouse gases, but China is fast catching up and is expected to become the world's largest producer of carbon dioxide some time this year.