“Dirty” or “very dirty”: These are the classifications of 46% of the world’s aquatic environments. The conclusion is from a survey that collected and organized data from 6,049 records of waste pollution in aquatic environments on all continents over the past decade.
The study, coordinated by researcher Italo Braga de Castro and led by doctoral student Víctor Vasques Ribeiro, from the Univisp Sea Institute (Federal University of São Paulo), analyzed articles published between 2013 and 2023 and calculated the level of cleanliness of rivers, estuaries, beaches and mangroves based on the Clean Coast Index (CCI), an international metric that measures the density of solid waste in coastal areas. Environments. The results were published in the Journal of Hazardous Materials.
The study indicated an uneven distribution of monitoring efforts. In this scenario, Brazil stands out, as it leads in the number of registrations in that period.
“But this does not guarantee that the environments monitored are in good, clean condition,” says Castro. “The results show that about 30% of Brazilian coastal environments were considered dirty or very dirty according to the CCI scale.”
One of the most serious cases of pollution has been found on Brazilian territory, and very close to the city of São Paulo, in the mangroves of Santos, which are among the most polluted points on the planet.
The global synthesis produced by the team showed a surprising homogeneity in the composition of waste, regardless of cultural, economic or geographical differences. Plastics and cigarette butts represent approximately 80% of the world’s waste.
“There are very few places that are completely litter-free,” the researcher comments.
Plastic materials represent 68% of registered materials. Their dominance is enhanced by their persistence in the environment, their fragmentation into micro- and nanoplastics, and their transport by ocean currents over large distances. Butts, responsible for 11% of waste, release more than 150 toxic substances that can be very harmful to aquatic organisms.
The study confirmed, with quantitative data, the positive role played by environmental protection areas.
“We analyzed 445 protected areas in 52 countries. The conclusion is unequivocal: protection reduces pollution by up to seven times. About half of the protected areas examined were classified as ‘clean’ or ‘very clean’. However, protection does not guarantee immunity in the face of increasing human pressure. About 31% of protected areas were classified as ‘dirty’ or ‘very dirty’, which shows that they are not effectively immune to waste pollution in the sea,” says Danilo Freitas. Rangel, a master’s student at Unifesp’s Marine Institute who participated in the research team.
A more complex result of the work is the so-called “edge effect” at the boundaries of conservation units. The team calculated the distance from each sampling point to the boundaries of protected areas, identifying a pattern: litter accumulates mainly at the edges, highlighting the direct impact of human activities in the surrounding area.
“This effect is reinforced by external pressures such as tourism, nearby urbanization and the transport of waste by rivers and ocean currents,” Castro emphasizes. “The fragility of the edges indicates the need for regional buffer policies, integrated management and supervision beyond the formal boundaries of conservation units.”
The study also innovated by blending pollution data with global social and economic indicators, using the Global Relative Deprivation Index (Global Relative Deprivation Index or GRDI) to estimate development levels at the scale of one square kilometre.
“We observed a non-linear pattern: in unprotected areas, pollution increases in the early stages of economic development, but begins to decline when the country reaches a certain level of infrastructure and environmental governance,” says Leonardo Lopez Costa, one of the authors of the study. “Within protected areas, development tends to increase pollution – a sign that investments in management and inspection are still unable to keep up with the speed of economic activity.”
Tackling waste pollution, especially plastics, relies on integrated actions across the entire production chain – from reducing manufacturing, through efficient collection and reuse systems, to multilateral agreements preventing cross-border movement of waste.
Without structural changes in global waste management, the crisis will worsen. In this context, one of the most important aspects of the study is its direct usefulness in ongoing international processes.
“The results provide an unprecedented scientific basis to support public policies and negotiations, such as the Global Plastics Treaty and the Kunming-Montreal Global Biodiversity Framework,” says Castro.
The study was supported by Fapesp (Fundação de Amparo à Pesquisa do Estado de São Paulo) through regular research grants awarded to Castro, a postdoctoral fellowship awarded to Costa and a doctoral fellowship awarded to Ribeiro
You can read the scientific article here