A map in which, at a glance, the concentration of heavy metals on the ground worldwide is observed. This is the main novelty of the study that has just published Science, conducted by a group of scientists led by Deyi Hou, from the Tsinghua University (China).
The study has been conducted From more than 1,400 regional studies and almost 800,000 existing samples. And, here is the second novelty, has used artificial intelligence techniques and automatic learning to map those areas that exceed risk thresholds for agricultural safety and human health. The study concludes that between 14 % and 17 % of cultivation lands – That is, about 242 million hectares worldwide – are contaminated, And between 900 and 1.4 billion people live in areas with high presence of heavy metals and metalloids such as cadmium, arsenic, cobalt, chrome, nickel or lead.
The authors warn that, although the presence of these metals is known, their worldwide distribution remains little known. According to the region, geology, weather, history and type of soil, a metal or another predominates, being the cadmium (in red on the map) the most abundant.
The presence of these elements may have natural or anthropogenic origin (mining, industry …). In countries such as Afghanistan, for example, there are areas with high concentrations of arsenic of natural origin dissolved in water, which is then absorbed by cultivated rice. «Fortunately, recent investigations have shown that certain types of iron or minerals in the soil can convert arsenito (a toxic and mobile form of arsenic) in arseniato, a less harmful way. This ‘invisible chemistry’ of the soil represents a security network, ”explains Jagannath Biswakarma, a researcher at the Cabot Institute for the Environment at the University of Bristol, in The Conversation. But, it is not necessary to go so far to find arsenic. «In some aquifers of Segovia or Valladolid it is naturally found in the sedimentary rock. In drought episodes, the population is recommended to consume bottled water to avoid their intake, ”says Ana Moliner Aramendía, of the Agrarian Production Department of the ETS of Agronomic, Food and Biosystem Engineering ETS of the Polytechnic University of Madrid.
Nickel, chromium, arsenic and cobalt also exceed security thresholds in several regions, due to a mixture of natural and human sources, such as mining or industry. In general, all living organisms need small amounts of certain metals such as cobalt, iron or manganese, which are usually obtained through food. But Some metals cause negative effects when their concentration in the body exceeds certain limits. «The most worried metal is cadmium, because it enters the human body through food. Phosphate fertilizers used in conventional agriculture usually contain cadmium. There are studies that consider it potentially carcinogenic, in addition to relating it to renal dysfunction and bone demineralization. Arsenic is associated with bladder cancer, cardiovascular diseases and diabetes. The study identifies a strip with high human activity in areas of ancient civilizations. In addition, he points out that in Europe, 28 % of the soils exceed the recommended threshold of metals, explains Carlos de Prada, environmental disseminator and responsible for the “homeless home” initiative.
Among the many studies that relate heavy metal with cancer, one stands out in Spain in 2018 by epidemiologists and geologists, which links deaths from esophageal cancer with high lead content, lung cancer with copper rich soils, brain tumors with arsenic and bladder cancer with cadmium. Although a direct causal relationship is not established, the need to investigate the influence of soil composition in tumors distribution is indicated. Prada insists that more studies are needed at the global level and better regulations, since the current ones do not contemplate the “cocktail effect or simultaneous and prolonged exposure to multiple substances.”
Amazonas and Mercury
The extraction of gold in the Amazon represents a particular case, due to the illegal activity close to commercial mines; Gold is sought using rudimentary methods and using mercury, an already prohibited metal and that is related to a typical disease of the British hatters, alluded to in Alicia in the Wonderland. The problem of soil pollution by metals and metalloids is that these do not disappear for decades, affecting ecosystems, fauna and food production. However, the researcher at the University of Bristol points out that “the soils have potential to heal” and remember that “food security begins on the ground.” In some cases, close to espíras or agricultural fields adjacent to former industrial complexes, programs of BIORREMEDIATION. “Near Murcia mines, plants are grown that partially absorb pollutants, and that are not destined to food, but to the wood or textile industry,” confirms Ana Moliner.
Other exposure routes
Another route of exposure to heavy metals is fish consumption, due to Bioacumulation of these pollutants in the marine environment. In 2008, the Catalan Food Security Agency published a study on its presence in fish and seafood of habitual consumption. They detected that the blue fish contained a metallic cocktail and not mercury, polychlorinated biphenyls, polyibromated diffenilic ethers, hexaclorobenzene, dioxins, furans and polychlorinated naphthalene. “As to arsenic, cadmium, lead and polycyclic aromatic hydrocarbons, more concentration in crustaceans and shellfish was observed», Says the report.
Another worrying case is that of lead, which can reach the human being through water pipes. In The US, about a year ago, the Government announced a plan to replace all existing lead pipes in ten years. The US Environmental Protection Agency (EPA) estimates that 8 % of the country’s pipes should be replaced. Lead is a neurotoxic that affects the central nervous system, digestive, kidneys, heart or reproductive system. “It has been suggested that it is behind Beethoven’s deafness and many studies associate it with aggressive behaviors in children and adolescents,” adds Prada.
An alert for the new mines
The authors of the study expect this work, which is in essence a compilation of previous works, serves as alert for political and farmers responsible to take measures and protect the soils. And it is published in a moment of growing demand for critical metals and mining reactivation. Europe wants in 2030 that at least 10 % of the consumption of essential raw materials comes from farms within its territory. The Commission has just published a list with the first 47 projects to extract, treat or recycle minerals such as Wolframio, Nickel, Zinc, Copper, Lithium or Strontium. Six are located in Spain: the Wolframium site of El Moto (Ciudad Real); Aguablanca, an old exploitation of nickel, copper and cobalt in Badajoz; Lithium in Las Navas (Cáceres); Wolframio in Almoharín (Cáceres); the circular recycling project in Huelva (centered in copper, nickel and metals of the platinum group); and the Las Cruces copper mine, in Seville, along with a new lithium mine in Doade (Galicia).