The new trend is a health and economic hazard and linked to exploding tourism in places like the Caribbean Sea and Pacific Ocean, the United Nations said in a report.
Garbage now rates among rising sea levels, overfishing and water shortages as a top danger to these small countries, and may be turning off tourists, the United Nations said.
The findings were released as environment ministers from around the globe gathered for the second day of a U.N. Environment Program summit dealing with water and sanitation. The summit ends Wednesday.
"Small islands across the Caribbean, Indian Ocean and the Pacific are some of the most vulnerable nations on Earth," UNEP executive director Klaus Toepfer said. "Handling solid wastes from industry, households and tourism is emerging as another issue with which they need advice and help."
Developing small island countries are burdened by an influx of tourism, but often lack the landfill space, expensive incinerators or treatment plants to deal with garbage and human waste.
Since the early 1990s, the level of plastic waste on small islands has increased fivefold, according to the UNEP study. In the Caribbean, about 90 percent of sewage is discharged untreated into surrounding seas; in the Pacific, about 98 percent.
Worldwide, about one in 20 people who go swimming in the oceans get sick because of such discharge, said Veerle Vandeweed, chief coordinator of the study.
Ironically, most of the environmental damage from tourism comes during the construction of resorts, not their operation, because of decisions to build too close to fragile coastlines and industrial waste, Vandeweed said. In the Caribbean alone, the number of tourists rose 19 percent to 17.1 million a year from 1993 to 1997.
The rapid development could backfire on the islands, if their allure as a tourist destination is spoiled by environmental degradation, UNEP warned.
The shoreline of the Pacific isle of Nauru, for example, appears blue-green in aerial photos, not from coral reefs, but from mounds of discarded beer cans, UNEP said.
The report found that in Samoa, creeks running into Apia harbor are "heavily choked with domestic rubbish adjacent to people's homes and the roadway." In Madagascar, 94 percent of waste and rubbish is never collected at all.
The piled-up trash also supports vermin such as rats, which carry such diseases as plague, scabies and other tropical sicknesses.
Economically, polluted coastal waters create oxygen-starved dead zones devoid of fish that undermine traditional island fishing industries.
The Alliance of Small Island States, a group of 45 island nations, is working with aid agencies, private industry and other governments to win access to better waste disposal technology and funding, chairman Jagdish Koonjul said.
"Many small island developing states … have launched public awareness campaigns and the people have responded," Koonjul said. "But the fact remains that unless you have ways of re-using and recycling rubbish, it is difficult to know what to do with materials such as plastics including plastic bags, aluminum and paper."
Sanitation problems are exacerbated on the islands because of the lack of fresh water. Rising ocean levels worldwide, triggered in part by global warming, have meant that freshwater wells are increasingly tainted with seawater, Koonjul said.
Globally about 1.1 billion people lack access to safe drinking water, while another 2.4 billion lacked access to basic sanitation, UNEP said. Nearly 5,000 children die every day from diseases caused by a lack of water.
The discussions in Jeju, a South Korean resort island, will form a basis for talks next month in New York with the U.N. Commission on Sustainable Development
That meeting will assess progress toward the United Nation's target of halving the number of people with no access to safe drinking water or basic sanitation by 2015.
The current forum will try to generate a Jeju Initiative that will identify concrete measures to be taken to reach those goals, UNEP spokesman Nick Nuttall said.
Supplying safe water is increasingly difficult because the world population is growing so fast, by about 77 million people a year, UNEP says.