Geographic Analysis of Motor Neuron Disease Mortality and Heavy Metals Released to Rivers in Spain

Abstract

The etiology of motor neuron disease (MND) is still unknown. The aims of this study were to: (1) analyze MND mortality at a fine-grained level; and (2) explore associations of MND and heavy metals released into Spanish river basins. MND deaths were extracted from the Spanish nationwide mortality registry (2007–2016). Standardized mortality ratios (SMRs) for MND were estimated at a municipal level. Sites that emitted quantities of heavy metals above the regulatory thresholds were obtained from the European Pollutant Release and Transfer Register database (2007–2015). The relative risks for non-exposed and exposed municipalities (considering a downstream 20 km river section) by type of heavy metal were analyzed using a log-linear model. SMRs were significantly higher in central and northern municipalities. SMRs were 1.14 (1.10–1.17) higher in areas exposed to heavy metals than in non-exposed areas: 0.95 (0.92–0.96). Considering the different metals, we found the following increased MND death risks in exposed areas: 20.9% higher risk for lead, 20.0% for zinc, 16.7% for arsenic, 15.7% for chromium, 15.4% for cadmium, 12.7% for copper, and 12.4% for mercury. This study provides associations between MND death risk and heavy metals in exposed municipalities. Further studies investigating heavy metal exposure are needed to progress in MND understanding.

A Comparison of Mercury Exposure from Seafood Consumption and Dental Amalgam Fillings in People with and without Amyotrophic Lateral Sclerosis (ALS): An International Online Case-Control Study

“…Our findings provide no evidence that mercury exposure from eating seafood or from dental fillings is related to ALS, but there remain other sources of mercury exposure that were not assessed in this study. For example, mortality rates from ALS have been found to higher in municipalities of Spain where levels above regulatory limits of heavy metals such as mercury are released into rivers [44]. Mercury is also used in many industrial applications, such as the production of chlorine gas and caustic soda, and is also present in thermometers, barometers, batteries, and electrical switches.…”

An overview on amyotrophic lateral sclerosis and cadmium

“…Exposure to heavy metals has been associated with the pathogenesis of ALS for over 150 years when heavy metals were detected in the tissues of patients with motor neuron diseases (MND) [40]. In Spain and France, three interesting studies have been carried out in the last 10 years to identify a relationship between exposure to environmental factors including heavy metals such as Cd and the onset of neurodegenerative diseases [39,41,42]. In particular, a French study analyzed the incidence of ALS within the region of Limousin, assessing the exposure of the population to environmental factors.…”

“…Numerous studies have examined the effects of heavy metals on neurodegenerative diseases [ 37 , 38 ]. Surveys have highlighted how the combination of geographical and epidemiological techniques was important for understanding the relationship between rare diseases and environmental exposure [ 39 ]. This fact linked with the unknown etiology of ALS leads researchers to speculate a relationship between the environment and its onset, including heavy metals.…”

“…It is interesting to note that municipalities with the highest number of ALS cases were more exposed to industrial activities; in fact, pulp and paper manufacturing industries have been significantly associated with a standardized incidence ratio (SIR) higher than 1 [ 41 ]. In 2018 in Spain, to identify the relationship between the occurrence of MND and exposure to heavy metals, the distribution of MND mortality rate in different municipalities over a period of 10 years was investigated by a spatial scale model [ 39 ]. The municipalities involved in the study were divided into exposed municipalities and unexposed municipalities, and results showed an increased risk of MND in exposed municipalities close to heavy metal emission sites.…”

“…The municipalities involved in the study were divided into exposed municipalities and unexposed municipalities, and results showed an increased risk of MND in exposed municipalities close to heavy metal emission sites. The study concluded that the combination of environmental emissions of different heavy metals including Cd (more than the single metal) was associated with a higher mortality rate (15.4%) in exposed sites than in control sites [ 39 ]. In the same year in Spain, a nested case-control study was conducted consisting of a retrospective cohort covering the entire region of Catalonia.…”