**3. Azores as a volcanic scenario**

The Azores archipelago is located in the North Atlantic Ocean, in the triple junction of the North American, African, and Eurasian plates [71–73]. The archipelago is formed by nine islands of volcanic origin that represent the emerged part of the Azores Plateau, a thick and irregular area of the oceanic crust roughly limited by the 2000-m bathymetric curve [74]. As a result of the Azores archipelago's location on an active plate boundary, frequent seismic and volcanic activity occurs, including volcanic eruptions and secondary manifestations of volcanism, such as hydrothermal vents and soil degassing processes.

São Miguel, the largest island of the archipelago, is formed by five active volcanic systems, including three central active volcanoes (Sete Cidades, Fogo and Furnas), separated by two fissure systems (Picos and Congro), and two extinct volcanic systems (Povoação and Nordeste) [75, 76].

Since the volcanic activity on the island contributes to a distinct soil elemental profile, resulting in a higher baseline for elements, the study of the baseline levels of TE is fundamental. When bioavailable to plants, animals, and humans, TEs can cause several diseases due to their elevated concentrations in soils. In addition, the high concentrations of some TEs in soils can inhibit the bioavailability of other elements, promoting the deficiency in elements that can be essential for plants, animals, and human health.

Considering that in this island, volcanic activity is usually in a quiescent phase, it presents itself as an ideal study scenario for an approach on environmental health problems, such as the exposure to toxic levels of TE and/or their deficiency.

#### **3.1 Distribution of TEs in São Miguel island soils**

In São Miguel island, with five active volcanic systems, all the soils have TE inputs resulting from the volcanic activity along the island. Nevertheless, in an island where the main income is agriculture, with the production of dairy, meat, and horticulture, little is known about the TE profile in these young volcanic soils.

In 2006, Amaral et al. [62] undertook a study to determine some baseline levels of trace elements in soils with different ages from active (Furnas; S. Miguel Island) and inactive volcanic sites (Santa Maria Island) of the Azores archipelago. These authors observed that, except for SiO2, Na2O, K2O, and Zn, the concentrations of major and trace elements were higher in Santa Maria soils. The authors point that these differences may be related to the higher capability of Santa Maria soils to retain the elements, given that these soils are richer in fine grain size particles, to retain those elements. In the study by Amaral et al. [63], using the earthworm *Lumbricus terrestris* as a model, the authors found that even though the volcanic site showed lower levels for most of the analyzed metals, the earthworms presented higher concentrations of the same TEs than those from the site without volcanic activity. These earthworms, with higher levels of trace metals, responded to this environment with higher bioavailability of TEs with a reduction of the thickness of the chloragogenous tissue and intestinal epithelium [63]. The higher bioavailability of TEs in these soils can be explained by the lower pH and clay content, as the authors suggested. Later on, a higher risk for uptake of potentially toxic metals in the active volcanic area was observed by Amaral et al. [77] when studying the scalp hair of men living in Furnas and in Santa Maria Island. The authors found that the scalp hair of men from Furnas had higher concentrations of Cd (96.9 ppb), Cu (16.2 ppm), Pb (3417.6 ppb), Rb (216.3 ppb), and Zn (242.8 ppm) when compared with men living in Santa Maria Island.

More recently, Parelho et al. [15] collected and analyzed soil samples from the farms of the main producers of vegetables in São Miguel island; these farms were located in the Picos Fissural Volcanic System, in the western half of the island. Results revealed that the TE background values fitted in the average values for European volcanic soils. However, this work showed that in addition to agricultural input there are elements of volcanogenic origin and that these specific soils tend to accumulate some trace metals due to their physicochemical properties.

Although these studies gather some information regarding the TE profile in the island volcanic soils, they were limited to areas of island without active volcanism and, therefore, TE contents may be even higher in the soils from where active manifestations of volcanism occur. Lately, there have been some studies that focused on the distribution of several TEs in all the volcanic complexes of São Miguel Island, evidencing a depletion of some TEs in the soils, such as iodine [55] and cobalt [78] and elevated concentrations of others, such as manganese [78].

#### **3.2 Iodine**

Iodine is a vital micronutrient required at all stages of life, with the fetal stage and early childhood being the most critical phases of requirement [79]. The connection between geological materials and TE deficiency is well documented for iodine since an inadequate intake of iodine results in disease conditions collectively known as Iodine Deficiency Disorders (IDD) [80]. The iodine overload is less common,

**109**

expected.

surveys.

2 ng/m3

related foods.

**3.3 Cobalt**

*Trace Elements in Volcanic Environments and Human Health Effects*

but can cause thyrotoxicosis as hyperthyroidism, chronic thyroiditis, Hashimoto's thyroiditis, and even may increase the risk of thyroid gland cancer [81–83]. Since the 1980s, the existence of health problems associated with iodine deficiency has been acknowledged. In 1986, Oliveira et al. [84] made a survey for endemic goiter on the island of São Miguel-Azores and observed that the median iodine intake ranged from 10 to 49 mg iodine/g creatinine, with a goiter prevalence usually greater than 20%. Later on, the studies by Limbert et al. [85, 86] established that urinary iodine deficiency was not only observed in children, but also in pregnant women. The most noteworthy fact of these studies was that the deficient iodine intake was not the same in all the islands of the Azores, with a positive highlight for the population of the island of Santa Maria, with mild deficiencies in iodine intake and, a negative one for the population of São Miguel, with severe

Since it is recognized that the ocean is the main reservoir of iodine and that the Azorean islands have geographical and climatic features that are clearly oceanic, Linhares et al. [55] investigated the environmental availability of iodine and bioavailability to human populations, especially in children at school age. This study reinforced the observations obtained in the previous studies [84, 86], revealing a deficient intake of iodine in the resident population of São Miguel Island, but it went further in the establishment of the causes. In this study, Linhares and the coauthors observed that the environmental availability of iodine was different in the soils from both islands, being significantly higher in the soils of Santa Maria than in São Miguel (58.12 ppm ± 40.94 vs. 14.53 ppm ± 11.79, respectively). The volcanic activity of São Miguel island; the islands' geomorphology; and consequently climate characteristics, such as orography and rainfall, are the main causes for the lower content of iodine in its soils. It must also be taken into account that the iodine soil content results from the complex dynamic balance of three processes: incorporation from the atmosphere, fixation, and volatilization. Soil characteristics, such as soil organic and inorganic components and the clay fraction, can affect iodine fixation. Higher concentrations of the organic and inorganic components and a higher clay content, as observed in Santa Maria island, provide a strong fixation of iodine in the soil, reducing the volatilization; therefore, in more mature volcanic soils (like those from Santa Maria) higher deposits of iodine are

The outcome of this last study reinforces the risk of iodine deficiency in São Miguel Island, emphasizing the necessity of introducing an iodine supplementation program in the population of this island, to overcome the low environmental availability of this halogen and its continued vigilance by periodic urinary iodine

Cobalt is usually found in the environment combined with other elements such as oxygen, sulfur, and arsenic. Small amounts of these chemical compounds can be found in rocks, soil, plants, and animals. The concentrations of cobalt in soil range from about 1 to 40 ppm and the amount of cobalt in the air is less than

. This specific TE has some notorious differences when compared with the remaining TEs; whereas the other elements are required in ionic form and are then converted into their metabolically active species, the body requires Co in a preformed compound, vitamin B12. The ability to synthesize vitamin B12 is only found in some bacteria, algae, and in some ruminants. Grazing cattle can synthesize vitamin B12 in the rumen, but in humans the main source of vitamin B12 is animal-

*DOI: http://dx.doi.org/10.5772/intechopen.90786*

deficiencies in iodine intake.

#### *Trace Elements in Volcanic Environments and Human Health Effects DOI: http://dx.doi.org/10.5772/intechopen.90786*

but can cause thyrotoxicosis as hyperthyroidism, chronic thyroiditis, Hashimoto's thyroiditis, and even may increase the risk of thyroid gland cancer [81–83].

Since the 1980s, the existence of health problems associated with iodine deficiency has been acknowledged. In 1986, Oliveira et al. [84] made a survey for endemic goiter on the island of São Miguel-Azores and observed that the median iodine intake ranged from 10 to 49 mg iodine/g creatinine, with a goiter prevalence usually greater than 20%. Later on, the studies by Limbert et al. [85, 86] established that urinary iodine deficiency was not only observed in children, but also in pregnant women. The most noteworthy fact of these studies was that the deficient iodine intake was not the same in all the islands of the Azores, with a positive highlight for the population of the island of Santa Maria, with mild deficiencies in iodine intake and, a negative one for the population of São Miguel, with severe deficiencies in iodine intake.

Since it is recognized that the ocean is the main reservoir of iodine and that the Azorean islands have geographical and climatic features that are clearly oceanic, Linhares et al. [55] investigated the environmental availability of iodine and bioavailability to human populations, especially in children at school age. This study reinforced the observations obtained in the previous studies [84, 86], revealing a deficient intake of iodine in the resident population of São Miguel Island, but it went further in the establishment of the causes. In this study, Linhares and the coauthors observed that the environmental availability of iodine was different in the soils from both islands, being significantly higher in the soils of Santa Maria than in São Miguel (58.12 ppm ± 40.94 vs. 14.53 ppm ± 11.79, respectively). The volcanic activity of São Miguel island; the islands' geomorphology; and consequently climate characteristics, such as orography and rainfall, are the main causes for the lower content of iodine in its soils. It must also be taken into account that the iodine soil content results from the complex dynamic balance of three processes: incorporation from the atmosphere, fixation, and volatilization. Soil characteristics, such as soil organic and inorganic components and the clay fraction, can affect iodine fixation. Higher concentrations of the organic and inorganic components and a higher clay content, as observed in Santa Maria island, provide a strong fixation of iodine in the soil, reducing the volatilization; therefore, in more mature volcanic soils (like those from Santa Maria) higher deposits of iodine are expected.

The outcome of this last study reinforces the risk of iodine deficiency in São Miguel Island, emphasizing the necessity of introducing an iodine supplementation program in the population of this island, to overcome the low environmental availability of this halogen and its continued vigilance by periodic urinary iodine surveys.

#### **3.3 Cobalt**

*Trace Metals in the Environment - New Approaches and Recent Advances*

**3.1 Distribution of TEs in São Miguel island soils**

with men living in Santa Maria Island.

Considering that in this island, volcanic activity is usually in a quiescent phase, it presents itself as an ideal study scenario for an approach on environmental health

In São Miguel island, with five active volcanic systems, all the soils have TE inputs resulting from the volcanic activity along the island. Nevertheless, in an island where the main income is agriculture, with the production of dairy, meat, and horticulture, little is known about the TE profile in these young volcanic soils. In 2006, Amaral et al. [62] undertook a study to determine some baseline levels of trace elements in soils with different ages from active (Furnas; S. Miguel Island) and inactive volcanic sites (Santa Maria Island) of the Azores archipelago. These authors observed that, except for SiO2, Na2O, K2O, and Zn, the concentrations of major and trace elements were higher in Santa Maria soils. The authors point that these differences may be related to the higher capability of Santa Maria soils to retain the elements, given that these soils are richer in fine grain size particles, to retain those elements. In the study by Amaral et al. [63], using the earthworm *Lumbricus terrestris* as a model, the authors found that even though the volcanic site showed lower levels for most of the analyzed metals, the earthworms presented higher concentrations of the same TEs than those from the site without volcanic activity. These earthworms, with higher levels of trace metals, responded to this environment with higher bioavailability of TEs with a reduction of the thickness of the chloragogenous tissue and intestinal epithelium [63]. The higher bioavailability of TEs in these soils can be explained by the lower pH and clay content, as the authors suggested. Later on, a higher risk for uptake of potentially toxic metals in the active volcanic area was observed by Amaral et al. [77] when studying the scalp hair of men living in Furnas and in Santa Maria Island. The authors found that the scalp hair of men from Furnas had higher concentrations of Cd (96.9 ppb), Cu (16.2 ppm), Pb (3417.6 ppb), Rb (216.3 ppb), and Zn (242.8 ppm) when compared

More recently, Parelho et al. [15] collected and analyzed soil samples from the farms of the main producers of vegetables in São Miguel island; these farms were located in the Picos Fissural Volcanic System, in the western half of the island. Results revealed that the TE background values fitted in the average values for European volcanic soils. However, this work showed that in addition to agricultural input there are elements of volcanogenic origin and that these specific soils tend to

Although these studies gather some information regarding the TE profile in the island volcanic soils, they were limited to areas of island without active volcanism and, therefore, TE contents may be even higher in the soils from where active manifestations of volcanism occur. Lately, there have been some studies that focused on the distribution of several TEs in all the volcanic complexes of São Miguel Island, evidencing a depletion of some TEs in the soils, such as iodine [55] and cobalt [78]

Iodine is a vital micronutrient required at all stages of life, with the fetal stage and early childhood being the most critical phases of requirement [79]. The connection between geological materials and TE deficiency is well documented for iodine since an inadequate intake of iodine results in disease conditions collectively known as Iodine Deficiency Disorders (IDD) [80]. The iodine overload is less common,

accumulate some trace metals due to their physicochemical properties.

and elevated concentrations of others, such as manganese [78].

problems, such as the exposure to toxic levels of TE and/or their deficiency.

**108**

**3.2 Iodine**

Cobalt is usually found in the environment combined with other elements such as oxygen, sulfur, and arsenic. Small amounts of these chemical compounds can be found in rocks, soil, plants, and animals. The concentrations of cobalt in soil range from about 1 to 40 ppm and the amount of cobalt in the air is less than 2 ng/m3 . This specific TE has some notorious differences when compared with the remaining TEs; whereas the other elements are required in ionic form and are then converted into their metabolically active species, the body requires Co in a preformed compound, vitamin B12. The ability to synthesize vitamin B12 is only found in some bacteria, algae, and in some ruminants. Grazing cattle can synthesize vitamin B12 in the rumen, but in humans the main source of vitamin B12 is animalrelated foods.

There are reports of health problems related to B12 deficiency, such as pernicious anemia and nerve damage [87, 88], and even psychical disorders, like impaired memory, irritability, depression, dementia, and psychosis [89].

Like iodine, cobalt deficiency has been long ago identified in São Miguel Island, particularly in grazing ruminants [90, 91]. However, it has been a subject of more interest only a few years ago, when Pinto [92] verified that approximately 40% of the dairy cattle in his study had deficient Co intake. These findings are extremely important for volcanic regions like the Azores, where livestock industries, such as dairy cattle farms, rely mostly on pasture grazing, where cattle are raised outdoors with an almost 100% natural diet of grass available in pastures.

To better understand the distribution of Co and its baseline levels on the island of São Miguel, Linhares et al. [78] collected soil samples from grazing sites through the island and observed a distinct pattern in the distribution. The highest concentrations of Co in soils were observed in the volcanic regions of Nordeste and Picos. These differences are related to the volcanic bedrock characteristics of the island; the Co content in the parental volcanic rocks is higher (20–58 mg/kg Co) in the low-silica rocks of Nordeste and Picos when compared to the high-silica rocks of the other volcanic regions. The differences within the volcanic regions of the island lie in the pedogenesis of parental volcanic materials; distinct geochemical compositions related to different degrees of magmatic evolution at depth result in different types of magma: (i) low-silica magmas (basalts and trachybasalts) as in Nordeste and Picos volcanic regions, that have high concentrations of iron, magnesium, chromium, nickel, and cobalt and; (ii) high-silica magmas (trachytes and rhyolites), such as Sete Cidades, Fogo/ Congro, and Povoação, that have low concentrations of these elements [93–95]. Linked to this, the existence of other TEs in the soils can also restrict the Co availability, as it happens with manganese (Mn) when present in high concentrations in the soils of São Miguel Island.

The study by Linhares et al. [78] revealed that the soils' volcanic origin (related to the parent rocks) and soil-forming processes affect the Co availability and, therefore, it is expected that severe Co deficiency can occur in most animals, especially the ones grazing in areas such as Furnas/Congro and Povoação.

The human dietary cobalt deficiency is unusual in individuals that consume animal-related food, fish, nuts, leafy green vegetables, such as broccoli and spinach, and cereals, including oats, since these are good food sources of cobalt [96].

In São Miguel Island, the lack of Co in soil assumes particular importance as the basis of the population feeding relies on locally produced agricultural products, and on meat and dairy products from grazing ruminants that are mainly fed with the available pasture grass in the grazing sites. Therefore, it is expected that, as observed in the ruminants, there might be some defined populated areas where the residents will have a deficient intake of Co and consequently may be more prone to develop several health problems associated with the lack of Co availability.

#### **3.4 Manganese**

Manganese (Mn) is a bioelement that has a cofactor function in the enzymatic processes [97]. It takes part in the functioning of antioxidant, musculoskeletal, immune, and reproductive systems and in detoxification processes [98]; nevertheless, excessive quantities of Mn cause toxic effects, especially in the central nervous system resulting in neurological diseases [99]. Manganese is ubiquitous in the environment, and human exposure arises from both natural and anthropogenic activities.

The Mn concentrations in soils strongly depend on the parent rock composition; the Mn contents in rocks can go from 174 mg/kg in sandstones to 1300 mg/kg in

**111**

(trachytes).

*Trace Elements in Volcanic Environments and Human Health Effects*

basalts, with an overall mean of 733 mg/kg Mn in the upper continental crust [100]. The Mn oxides in soils have very high sorption ability and they can accumulate ions from the soil solution; these oxides have a strong affinity for Co ions, which can

The human exposure to Mn occurs mainly by ingestion; this TE is naturally present in a wide variety of foods, including whole grains, clams, oysters, mussels, nuts, soybeans and other legumes, rice, leafy vegetables, coffee, tea, and many spices [101, 102]. Manganese is absorbed in the small intestine and, after absorption, some Mn remains free, but most of it is bound to transferrin, albumin, and plasma alpha-2-macroglobulin. Mn deficiency is very rarely observed in humans but cases of Mn toxicity have been reported. Mn toxicity can be related to the dietary Mn intake and to chronic environmental exposure in welding and mining sites, as the inhalation of Mn dust can be toxic [103]. Mn toxicity affects the central nervous system and can cause tremors, muscle spasms, tinnitus, and hearing loss [101, 102]. Mn toxicity can also cause "manganism," a neurodegenerative disease with symptoms that resemble Parkinson's disease [104] and "Machado Joseph Disease (MJD)," a progressive

In the Azores, there are few studies focusing on Mn availability and its effects. The existing studies focus on the assessment of Mn concentration in hydrothermal vents, as tracer of hydrothermal activity intimately related to mid-ocean ridge processes [106] and the Mn bioaccumulation in marine species, such as *Cystoseira abies-marina* [107]. Regarding the assessment of Mn in soils, the most recent studies are orientated to vineyard soils in the islands of Terceira, Graciosa, and Pico. Lima et al. [108] revealed that the Mn concentration in the soils of cultivated vines was 692.5 mg/kg in Pico, 1023.8 mg/Kg in Terceira, and 2041.6 mg/kg in Graciosa,

More recently, in a survey to access cobalt concentration in volcanic soils to predict the risk of cobalt deficiency [78], the concentration of Mn was also determined as it can affect Co bioavailability. These authors verified an uneven distribution of Mn in the defined volcanic regions of the island; the highest Mn concentrations were observed in Nordeste and Picos (1782.50 mg/kg ± 108.98 and 1461.11 mg/ kg ± 63.93, respectively), while the lowest concentrations were observed in the soils of Povoação and Furnas/ Congro (874.88 mg/kg ± 78.52 and 746.25 mg/kg ± 209.07, respectively). As observed for Co, the Mn concentration in soil is strongly associated with their content in the parental volcanic rocks. Therefore, low-silica magmas (basalts) of Nordeste and Picos have higher contents of Mn when compared to Furnas/ Congro and Povoação parent volcanic rocks formed by high-silica magmas

The most noteworthy aspect of the Mn concentration in the volcanic soils of São Miguel island is that all the volcanic regions have concentrations above the estimated background mean of the European soils (524 mg/kg) [24] and that in most grazing sites the measured concentrations were higher than 900 mg/kg (upper limit threshold) [Linhares et al. (unpublished data)]. Considering that high concentrations of Mn can be associated with the Machado Joseph disease [105, 108], this scenario undertakes a singular meaning in the Azorean context. There are two major ancestral origins: (1) a worldwide-spread haplotype, TTACAC

or the Joseph lineage, and (2) a more recent one, GTGGCA or the Machado lineage, seen mostly in Portuguese people [109, 110], being associated with families with MJD from the Portuguese Azorean islands of Flores and São Miguel (respectively, the birthplace of the Joseph and the Machado kindreds). Nowadays, the Azorean group remains the most important cluster of this disease, with 32 extended MJD families with origins in Flores, S. Miguel, Terceira, and Graciosa islands [111]. In Flores Island, the prevalence of the disease has been decreasing

*DOI: http://dx.doi.org/10.5772/intechopen.90786*

reduce Co availability to plants.

spinocerebellar ataxic disorder [105].

evidencing significant differences between these islands.

#### *Trace Elements in Volcanic Environments and Human Health Effects DOI: http://dx.doi.org/10.5772/intechopen.90786*

*Trace Metals in the Environment - New Approaches and Recent Advances*

with an almost 100% natural diet of grass available in pastures.

high concentrations in the soils of São Miguel Island.

the ones grazing in areas such as Furnas/Congro and Povoação.

There are reports of health problems related to B12 deficiency, such as pernicious anemia and nerve damage [87, 88], and even psychical disorders, like impaired memory, irritability, depression, dementia, and psychosis [89].

Like iodine, cobalt deficiency has been long ago identified in São Miguel Island, particularly in grazing ruminants [90, 91]. However, it has been a subject of more interest only a few years ago, when Pinto [92] verified that approximately 40% of the dairy cattle in his study had deficient Co intake. These findings are extremely important for volcanic regions like the Azores, where livestock industries, such as dairy cattle farms, rely mostly on pasture grazing, where cattle are raised outdoors

To better understand the distribution of Co and its baseline levels on the island of São Miguel, Linhares et al. [78] collected soil samples from grazing sites through the island and observed a distinct pattern in the distribution. The highest concentrations of Co in soils were observed in the volcanic regions of Nordeste and Picos. These differences are related to the volcanic bedrock characteristics of the island; the Co content in the parental volcanic rocks is higher (20–58 mg/kg Co) in the low-silica rocks of Nordeste and Picos when compared to the high-silica rocks of the other volcanic regions. The differences within the volcanic regions of the island lie in the pedogenesis of parental volcanic materials; distinct geochemical compositions related to different degrees of magmatic evolution at depth result in different types of magma: (i) low-silica magmas (basalts and trachybasalts) as in Nordeste and Picos volcanic regions, that have high concentrations of iron, magnesium, chromium, nickel, and cobalt and; (ii) high-silica magmas (trachytes and rhyolites), such as Sete Cidades, Fogo/ Congro, and Povoação, that have low concentrations of these elements [93–95]. Linked to this, the existence of other TEs in the soils can also restrict the Co availability, as it happens with manganese (Mn) when present in

The study by Linhares et al. [78] revealed that the soils' volcanic origin (related to the parent rocks) and soil-forming processes affect the Co availability and, therefore, it is expected that severe Co deficiency can occur in most animals, especially

The human dietary cobalt deficiency is unusual in individuals that consume animal-related food, fish, nuts, leafy green vegetables, such as broccoli and spinach,

In São Miguel Island, the lack of Co in soil assumes particular importance as the basis of the population feeding relies on locally produced agricultural products, and on meat and dairy products from grazing ruminants that are mainly fed with the available pasture grass in the grazing sites. Therefore, it is expected that, as observed in the ruminants, there might be some defined populated areas where the residents will have a deficient intake of Co and consequently may be more prone to

Manganese (Mn) is a bioelement that has a cofactor function in the enzymatic processes [97]. It takes part in the functioning of antioxidant, musculoskeletal, immune, and reproductive systems and in detoxification processes [98]; nevertheless, excessive quantities of Mn cause toxic effects, especially in the central nervous system resulting in neurological diseases [99]. Manganese is ubiquitous in the environment, and human exposure arises from both natural and anthropogenic

The Mn concentrations in soils strongly depend on the parent rock composition; the Mn contents in rocks can go from 174 mg/kg in sandstones to 1300 mg/kg in

and cereals, including oats, since these are good food sources of cobalt [96].

develop several health problems associated with the lack of Co availability.

**110**

activities.

**3.4 Manganese**

basalts, with an overall mean of 733 mg/kg Mn in the upper continental crust [100]. The Mn oxides in soils have very high sorption ability and they can accumulate ions from the soil solution; these oxides have a strong affinity for Co ions, which can reduce Co availability to plants.

The human exposure to Mn occurs mainly by ingestion; this TE is naturally present in a wide variety of foods, including whole grains, clams, oysters, mussels, nuts, soybeans and other legumes, rice, leafy vegetables, coffee, tea, and many spices [101, 102]. Manganese is absorbed in the small intestine and, after absorption, some Mn remains free, but most of it is bound to transferrin, albumin, and plasma alpha-2-macroglobulin. Mn deficiency is very rarely observed in humans but cases of Mn toxicity have been reported. Mn toxicity can be related to the dietary Mn intake and to chronic environmental exposure in welding and mining sites, as the inhalation of Mn dust can be toxic [103]. Mn toxicity affects the central nervous system and can cause tremors, muscle spasms, tinnitus, and hearing loss [101, 102]. Mn toxicity can also cause "manganism," a neurodegenerative disease with symptoms that resemble Parkinson's disease [104] and "Machado Joseph Disease (MJD)," a progressive spinocerebellar ataxic disorder [105].

In the Azores, there are few studies focusing on Mn availability and its effects. The existing studies focus on the assessment of Mn concentration in hydrothermal vents, as tracer of hydrothermal activity intimately related to mid-ocean ridge processes [106] and the Mn bioaccumulation in marine species, such as *Cystoseira abies-marina* [107]. Regarding the assessment of Mn in soils, the most recent studies are orientated to vineyard soils in the islands of Terceira, Graciosa, and Pico. Lima et al. [108] revealed that the Mn concentration in the soils of cultivated vines was 692.5 mg/kg in Pico, 1023.8 mg/Kg in Terceira, and 2041.6 mg/kg in Graciosa, evidencing significant differences between these islands.

More recently, in a survey to access cobalt concentration in volcanic soils to predict the risk of cobalt deficiency [78], the concentration of Mn was also determined as it can affect Co bioavailability. These authors verified an uneven distribution of Mn in the defined volcanic regions of the island; the highest Mn concentrations were observed in Nordeste and Picos (1782.50 mg/kg ± 108.98 and 1461.11 mg/ kg ± 63.93, respectively), while the lowest concentrations were observed in the soils of Povoação and Furnas/ Congro (874.88 mg/kg ± 78.52 and 746.25 mg/kg ± 209.07, respectively). As observed for Co, the Mn concentration in soil is strongly associated with their content in the parental volcanic rocks. Therefore, low-silica magmas (basalts) of Nordeste and Picos have higher contents of Mn when compared to Furnas/ Congro and Povoação parent volcanic rocks formed by high-silica magmas (trachytes).

The most noteworthy aspect of the Mn concentration in the volcanic soils of São Miguel island is that all the volcanic regions have concentrations above the estimated background mean of the European soils (524 mg/kg) [24] and that in most grazing sites the measured concentrations were higher than 900 mg/kg (upper limit threshold) [Linhares et al. (unpublished data)]. Considering that high concentrations of Mn can be associated with the Machado Joseph disease [105, 108], this scenario undertakes a singular meaning in the Azorean context. There are two major ancestral origins: (1) a worldwide-spread haplotype, TTACAC or the Joseph lineage, and (2) a more recent one, GTGGCA or the Machado lineage, seen mostly in Portuguese people [109, 110], being associated with families with MJD from the Portuguese Azorean islands of Flores and São Miguel (respectively, the birthplace of the Joseph and the Machado kindreds). Nowadays, the Azorean group remains the most important cluster of this disease, with 32 extended MJD families with origins in Flores, S. Miguel, Terceira, and Graciosa islands [111]. In Flores Island, the prevalence of the disease has been decreasing

through the years but MJD still reaches its highest worldwide value (1:239), constituting a public health problem [112].

In 2004, Purdey [105] established a common abnormal hallmark of high manganese (Mn)/low magnesium (Mg) status and suggested that this aberrant mineral ratio inactivates the Mn/Mg catalyzed endonuclease-1 enzyme. The high Mn/low Mg rate observed in all volcanic regions of São Miguel Island reinforces the need for further studies in these elements as they are intimately related to MJD.

These studies evidence that the Azores archipelago presents itself as an ideal scenario for the study of TE availability and possible health effects. However, the total TE concentration in soil is a relatively weak measure of their bioavailability. Given that the bioavailability depends on specific soil characteristics, such as organic matter content and pH, similar concentrations of TEs in different soils may not have the same bioavailability.

The assessment of TE bioavailability is fundamental, as the bioavailable fraction of trace elements is the fraction most likely to harm plants and animals. Consequently, the impact of TEs on soil and the surrounding environment cannot be predicted by measuring the total concentration of elements *per se*, since only the soluble and mobile fraction has the potential to leach or to be taken up by plants and enter the food chain [113]. Future studies should consider the assessment of the bioavailable part of the TEs in volcanic environments, to define remediation strategies in order to prevent health problems associated with TE depletion or excessive intake.
