The question of whether microplastics in the Pantanal, South America, are a threat to humans is explored here in detail by Pierre Girard, PhD.1, 2, Érika de Faria, PhD (in progress)2, and Andressa C. Moreschi PhD (in progress)2
Microplastics are found everywhere: from pole to pole, in all oceans, in food, in water, and the human gut. The question is not anymore if there are or not microplastics at any place. It is more about how much there are, and if the concentrations at which they are encountered at any place can harm people, living beings and reduce the provision of ecosystems services sustaining human life and wellbeing.
Most commonly microplastics found in the environment are described as microspheres, fragments and microfibres smaller than 5mm. Microspheres are generally associated with cosmetics, fragments are thought to result from abrasion and degradation of larger macroplastics while microfibres come from the laundering of synthetic textiles. Microfibres are the most common microplastics found in freshwaters.
The World Health Organization (WHO) recently stated that microplastics in drinking water don’t appear to pose a health risk at current levels. But WHO cautions that more research is needed to assess their potential impacts on human health. Current research suggests microplastics as vectors for transferring a variety of contaminants, including bacteria, viruses, endocrine disruptors, etc. At this stage, there is still no consensus about health effects for humans.
Studies show microplastics and associated contaminants can harm organisms such as commercial fish, but there is still very little knowledge about the effect of microplastics at the level of food webs and ecosystems. Nevertheless, they may reduce ecosystem service provisions related to fisheries, heritage and charismatic species, and recreation leading to implications for human health and wellbeing.
Microplastic contamination in the Pantanal
The Pantanal, located in central South America, is a vast wetlands mosaic larger than England and is formed by the coalescing floodplains of the Paraguay River and its tributaries. These rivers all flow in the Upper Paraguay Basin (UPB). The Pantanal lowlands are surrounded by plateaus where most cities and human activities occur. It is home to about 3 million people who live mostly from cattle ranching, tourism and fishing. On the surrounding plateaus, industrial agriculture (soy, corn, cotton) is the main economic activity. Metropolitan Cuiabá is the largest city in the UPB with about 800 thousand people and is built on the margin of the Cuiabá River, the largest Paraguay tributary. Many streams and brooks are borne in this urban area and are flowing to the Cuiabá River.
Microplastics were found in this streams’ network in a concentration similar to what has been found in Chinese, European and North American cities. Microfibres make >80% of all microplastics in the metropolitan Cuiabá and were associated with the direct discharge of laundering sewage in surface waters. Less than 55% of the sewage is collected and treated in metropolitan Cuiabá.
Microplastics were also found in the Cuiabá River waters at various locations. Their concentrations decrease downstream from the metropolitan area. In the urban area, microplastics concentrations are four times larger than 230 km downriver, into the Pantanal, where they vary from 20 to 70 particles per cubic metre. Microplastics were also found in similar content in lakes adjacent to the Paraguay River about 50 km upriver from Corumbá, the closest city. As well as upriver, microfibres dominate the microplastics load. Concentrations in the Pantanal are an order of magnitude higher than what has been found in Tampa Bay, Florida, but also a few orders of magnitude lower than in the Pearl River Estuary, China, and similar to what have been found in the Seine River in France for example.
Laboratory experiments have also shown that local bivalves were taking up microplastics particles suspended in the water column. A small fraction of these particles were retained in their tissues, while most of the microplastics found their way in the excreta and deposited at the bottom. This is an indication that, as elsewhere in freshwater environments, microplastics can enter the local food web. Research is underway to assess microplastics in the Pantanal sediments.
This quick portrait of the current knowledge on microplastics in the Pantanal suggests that microplastics are coming from up rivers urban areas. However, floodplains derived microplastics, mainly linked to tourism, may also contribute to the microplastics load, especially where larger concentrations are found. This portrait also reveals that, even in remote, infrequently visited and inaccessible locations within the Pantanal, there are microplastics in rivers, lakes and floodwaters.
Are humans threatened by microplastics in the Pantanal? Still a big unknown
At this stage, what seems clear, with the current knowledge regarding microplastic contamination in the Pantanal surface waters is that they do not pose a direct threat to human health. However, as in other regions, it is not known yet if present contamination levels could disturb food webs and reduce the provision of services offered by the Pantanal ecosystems. The most vulnerable human communities living in these wetlands depend on what they fish for their daily proteins and to generate a little extra income. Tourism also builds on fishing, but as well on the sighting of aquatic birds and large mammals, such as jaguars and otters. Commercial fishes, aquatic birds, and large mammals sit close to the top of food chains. Can microplastics accumulate along these food chains and reach harmful concentrations for humans? Or, similarly, can they attain toxic levels in food webs, resulting in a reduction of the populations of aquatic birds or mammals which draw many tourists annually and generate revenue? Likewise, what do upriver urban areas contribute in proportion to the total microplastics load in the Pantanal? And what fraction of this contamination is due to tourism? Finally, the relative importance of microplastic contamination regarding other Pantanal ecosystem stressors is a question that remains to be answered. More research and research funds are urgently needed to resolve these interrogations and orient meaningful policies to preserve human wellbeing in the Pantanal.
(1) Pantanal Research Center, Cuiabá, MT, Brazil.
(2) Bioscience Institute, Federal University of Mato Grosso, Cuiabá, MT, Brazil.
Please note: This is a commercial profile