Washington (AFP) - Prince Charles made an impassioned speech in Washington about the deteriorating state of the world's oceans, striking a somber note on the first full day of his US tour with wife Camilla.
A vociferous environmental campaigner, the Prince of Wales told government, corporate and non-profit leaders at a hotel Wednesday in the US capital: "One issue that we absolutely cannot ignore is that of the increasing quantity of plastic waste in the marine environment.
"I was horrified to learn that, according to recent research, we collectively allow as much as eight million tonnes of plastic to enter the oceans every year."
The prince said he was "haunted by the tragic images of seabirds, particularly albatrosses, that have been found dead, washed up on beaches after mistaking a piece of plastic for a meal."
Earlier, in lighter scenes, the royal couple mingled with gobsmacked young Americans as they hit some of Washington's top tourist attractions.
Bright sunlight but chilly temperatures prevailed as they inspected the Lincoln Memorial and Martin Luther King monument.
Later they ventured out to Mount Vernon to look around George Washington's patrician home, which commands a grand view over the lower Potomac.
Prince Charles, 66, also took time to inspect the National Archives' copy of the Magna Carta, signed eight centuries ago this year by his predecessor, England's King John.
They will drop in on President Barack Obama and Vice President Joe Biden in the Oval Office on Thursday, part of a whirlwind tour intended to promote the US-British partnership in such areas as climate change, opportunity for youth and responsibility in world affairs.
It is the 20th official visit to the United States for Charles, who is assuming more and more of the duties once undertaken by his elderly mother.
- 'What's he the prince of?' -
At the Lincoln Memorial, two historians explained how American schoolchildren memorize the Gettysburg Address, inscribed in its Grecian stone walls.
Perhaps not surprisingly in a republic besotted by royalty, cheers rang out when school groups spotted Charles and Camilla, 67, coming down the stairs.
Prompted by a yell from an eighth-grade math teacher from North Carolina, they spent about five minutes chatting with youthful members of the crowd.
"I was excited. He looks very important," Jasper Tahnk, 14, from Boston, told AFP after he was asked by the prince if he was on some kind of school break.
Others were less impressed. "What's he the prince of?" asked Pierce Riddick, 14.
From there it was on to rural Mount Vernon, which Charles last visited in 1970 when he traveled to the United States with his sister Princess Anne.
Charles and Camilla laid a wreath at the tomb of America's revolutionary war hero and first president and signed their names in a guest book -- something Mount Vernon staff promptly shared via social media.
One young visitor from West Virgina was so excited to relay the news of the royal guests to her Twitter pals that she confused Camilla for mother-in-law Queen Elizabeth II, who turns 89 next month.
- Special gifts -
At the National Archives, Charles looked delighted when he got not one, but two gifts that spoke to him personally.
One was a patent issued in 1931 to his beloved great uncle, Lord Louis Mountbatten, for a new and improved polo stick.
The other was a 1957 official cable from London to the US State Department, enquiring about "engine specifications" for a "midget car" that had been gifted to the prince, then eight years old.
The prince laughed heartily at the cable.
The royal couple flew into the US on Tuesday for a visit that will also take them to Kentucky on Friday.