In agriculture, large quantities of chemicals are used to accelerate plant growth, optimize harvests, and prevent pests, weeds, and other harmful substances. For all these activities, chemicals are applied to the crops. These chemicals fall into the soil and are absorbed by it. What many don't realize is that these nitrogenous products end up contaminating the groundwater from which we draw our drinking water.
Heavy rainfall events, like those we've experienced in recent months, carry larger quantities of these chemicals, which are harmful to human health. These chemicals are then washed into the Mar Menor lagoon . What can be done to prevent them from reaching the lagoon?
Chemicals banned by the European Union
Pesticides, herbicides, organic fertilizers, and some industrial additives are the main products used on crops. Many of these chemicals are highly toxic to human health and have been banned by the European Union.
In recent cases, such as the Mar Menor lagoon, torrential rains have washed these pesticides into the water, prompting authorities to implement controls at the source to prevent further contamination. However, a ban is not always enough without strict enforcement measures.
A 2017 study by the Murcia Oceanographic Center investigated the presence of pesticides in the Mar Menor sediments during 2009 and 2010. Scientists Rubén Moreno-González and VÃctor Manuel León analyzed how heavy rainfall influenced the concentration of these pollutants. The study, published in Environmental Science and Pollution Research , concluded that most of the pesticides arrived via the El Albujón ravine.
What exactly chemicals are dumped into the Mar Menor?
Among the pesticides detected in the Mar Menor, the study highlighted terbuthylazine, chlorpyrifos , and tributyl phosphate . Terbuthylazine is a herbicide banned in the EU. It has been linked to carcinogenic effects, endocrine disruption, and neurotoxicity. Despite its ban, it continues to be found in concentrations exceeding permitted levels due to runoff from rainwater.
Chlorpyrifos , a highly toxic insecticide, was also detected in large quantities. This chemical has been a source of concern due to its negative impact on aquatic organisms and has been banned in several EU regions. Tributyl phosphate , an additive used in aircraft engines and industrial sectors, has also been banned due to its toxicity.
These chemicals are transported to the Mar Menor through the El Albujón, Miranda and La Maraña gullies, as well as through the Hita beach and other drainage channels. It is crucial to create barriers that prevent these products from reaching the water in the first place.
How do we prevent these pollutants from reaching the Mar Menor?
To prevent the impact of these chemicals on marine ecosystems, it is essential to address the problem at its source. Restrictions on the use of certain pesticides must be stricter, but efforts must also be made to educate farmers about the cumulative impact of these products on the environment.
Pesticides are not only harmful on their own, but when combined, their negative effects are amplified. This interaction is known as synergy . To protect the Mar Menor, it is essential to:
- Avoid surface runoff.
- Monitoring the impact of contaminated groundwater.
- Prevent atmospheric deposition of pollutants.
Solutions must be comprehensive and based on a clear legislative framework. The use of products already identified as dangerous must be prohibited in areas such as the reed beds of the Mar Menor and Campo de Cartagena. Treatment wetlands and filtration systems must also be established to purify agricultural water before it reaches the lagoon.
Another important aspect is the sedimentation of pollutants. Rainy episodes not only bring new chemicals to the lagoon, but also remove old sediments, releasing old pollutants. One study mentioned that after episodes of intense rain, large quantities of heavy metals that had been trapped at the bottom of the Mar Menor were released. This process makes recovery even more difficult.
The importance of control over discharges
The most recent studies point to the key role played by drainage systems and treatment plants in the arrival of pollutants to the Mar Menor. The management of industrial waste, together with the handling of poorly treated wastewater, frequently occurs in areas close to the lagoon, also increasing the risk of contamination.
It is essential to conduct regular assessments of the condition of wastewater treatment plants and ensure that permitted discharge limits are not exceeded. In some cases, high levels of ammonia and other chemicals have been detected, which can also exacerbate the eutrophication problem. When mixed with agricultural pesticides, these substances create a toxic cocktail that amplifies the effects on marine life.
To mitigate these events, the implementation of denitrification infrastructure in key areas around the Mar Menor is suggested . These systems would help filter excess nutrients before they reach the water bodies.
Eutrophication: the great danger for the Mar Menor
Eutrophication is a phenomenon that occurs when a body of water suffers an excess of nutrients, primarily nitrogen and phosphorus, leading to an excessive proliferation of algae. This blocks sunlight and reduces available oxygen, causing the death of plants and animals in the deeper layers.
The Mar Menor has suffered several episodes of eutrophication in recent years, the most famous being the green soup of 2016 , which destroyed up to 90% of the meadows of macroalgae and phanerogams that inhabited the bottom of the lagoon.
The effects of this crisis are still being felt today, as the most vulnerable marine species, such as the seahorse, have dramatically declined in number.
Rainfall and runoff carry large quantities of nitrogen and phosphates from agricultural areas, exacerbating this problem. Therefore, it is necessary to implement a preventative system that includes both soil and water protection.
What future awaits the Mar Menor?
The situation in the Mar Menor is critical, but not irreversible. There are multiple solutions that, if implemented correctly and urgently, could stop the damage and allow the ecosystem to begin to recover.
The first step is to cut off the entry of nutrients and chemicals into the lagoon by improving control over agriculture, sewage treatment plants and other sources of pollution. In parallel, scientific studies must continue to provide data to better understand the dynamics of this coastal lagoon and apply evidence-based solutions.
With political will and decisive measures , the Mar Menor can begin to recover in the coming years. Numerous examples of the recovery of coastal ecosystems affected by eutrophication in other parts of the world demonstrate that this process, although complex, is possible. However, it is essential that action be taken as soon as possible to prevent a total collapse of the ecosystem.