Mercury and Cadmium contamination in ethnic groups from the Colombian Amazon: A panoramic overview of exposure sources and the general health status of the population.
Alcalá Orozco, María Clara | 2020
Environmental exposure to heavy metals such as mercury (Hg) and
cadmium (Cd) is currently a worldwide public health problem,
especially in biodiversity hotspots such as the Amazon River basin,
which houses large aquatic complexes, including the Amazon and
Putumayo Rivers. These water bodies and their main tributaries are
extensively degraded and threatened by dams, mining, and
deforestation. In these areas, artisanal and small-scale gold mining
activities are key contributors to Hg pollution in ecological media, as
this element is employed for the separation of gold particles through
an amalgamation process. In addition, human populations are highly
exposed to other heavy metals, most significantly Cd, as it is likely
mobilized during mining activities.
In addition to mining, the Colombian Amazon faces a significant
disappearance of forest mass as a result of the conversion of land into
agricultural plantations or grazing areas, logging, and road
construction, which is carried out illegally or, at least, irregularly in
many cases. This situation co-exists with other issues that are due to
poverty, and which, in turn, lead to micronutrient deficiencies,
including Se. Unfortunately, this panorama represents a risk to the
health of indigenous communities that not only base their diet and
economy on the cultivation of autochthonous species, but also on the
consumption of fresh and canned fish as main sources of protein.
Given the risks that heavy metals represent to human health,
biological indicators are essential tools in the assessment of health
issues generated by exposure to them. These indicators, when
associated with the socio-demographic characteristics of the
population, the frequency of fish consumption, the diet, and the
specific symptomatology related to heavy metal exposure; provide
valuable information that can be used to estimate risks to the health
of vulnerable communities. Although multiple studies have shown
levels of Hg and Cd contamination in the Amazon region, few have
focused on the relationship between these concentrations, the load of
the essential element Se, and their effects on exposed individuals (i.e.
changes in the hematological parameters of populations).
In order to understand the current state of Hg contamination in the
Colombian Amazon, the first study in this thesis documented
concentrations of this element in nine indigenous communities of the
Tarapaca Village (on the Cotuhe and Putumayo rivers), an area
inhabited by groups that have a traditional lifestyle that is highly
affected by the mining activities carried out there. Subsequently, hair
and fish samples were taken from residents of the Municipality of
Puerto Nariño, which is located at the southern extreme of the
Colombian Amazon, in order to evaluate the interactions between Hg,
Cd and Se, and possible risks and associated with changes in the
hematological levels of the population. Likewise, the isotopic
composition of Hg of the inhabitants of this municipality was
evaluated in order to confirm that their exposure to this element
occurred through the consumption of fish, thus highlighting the
influence of gold mining in this area. Finally, additional results are
presented related to the presence of As and Pb, as well as eight
essential elements in brands of canned tuna and sardines consumed
by the inhabitants of this region.
In order to meet these objectives, a total of 190 hair samples were
taken from indigenous people living at the Tarapaca village. The
overall mean T-Hg level of these samples was 10.6±0.4 μg/g, with
values ranging from 0.61 to 31.1 μg/g. Based on recommendations
from the United States Environmental Protection Agency (USEPA),
99.5% of the samples exceeded the maximum level of 1.0 μg/g Hg.
This Hg content was significantly associated with fish consumption
(ρ=0.253; p<0.001), and, according to a health survey that was
simultaneously conducted, at least 24.7% of the volunteers
manifested some signs and symptoms related to Hg poisoning. Thus,
this study demonstrates the extensive Hg contamination currently
found in the Colombian Amazon environment, a situation that could
impact the quality of life of its vulnerable indigenous groups.
In the context of the second project that was carried out, Hg, Cd, and
Se concentrations in fish, as well as the magnitude of exposure and
hematological conditions of adult citizens from Puerto Nariño
(Colombian Amazon) were assessed. Among fish samples, greater Hg
concentrations were found in higher trophic level species, including
Rhaphiodon vulpinus (880±130 ng/g) and Pseudoplatystoma tigrinum
(920±87 ng/g). These species presented both the highest hazard
quotients and the lowest Se:Hg molar ratios found in the study;
conditions that may represent significant health risks. Several
samples of Mylossoma duriventre and Prochilodus magdalenae had Cd
levels greater than the recommended limits. Mercury concentrations
in human hair and blood were 5.31 µg/g and 13.7 µg/L, respectively.
All hair samples exceeded the 1.0 μg/g threshold set by the USEPA,
whereas 93% of the volunteers had Hg levels in blood above 5 μg/L,
suggesting that there is elevated exposure in the Amazon
environment. In relation to Cd, the mean value found in the blood of
the volunteers was 3.1 µg/L, with 21% of samples surpassing 5 µg/L.
Additionally, eighty-four percent of participants presented Se
deficiencies (<100 μg/L). There was also a significant association
between fish consumption and T-Hg in hair (ρ=0.323; p=0.032) and
blood (ρ=0.381; p=0.011). In this last matrix, Se correlated with Cd
content, whereas lymphocytes were inversely linked to Hg
concentrations. The results of this study showed that there was
extensive exposure to Hg through fish consumption in this
population, which may be linked to negative impacts on hematology
parameters within the community.
Given that hair reflects the body's load of Hg, in the third project, Hg
stable isotopes in hair were used as tracers of potential sources of
this element, taking the indigenous communities from Pueblo Bello
(Sierra Nevada de Santa Marta) as comparison populations. The slope
obtained for hair samples from Pueblo Bello (1.197±0.050, 2SE, n=36)
and the Δ199Hg and Δ201Hg anomalies indicated that the Hg levels
within the population are mostly the result of a photochemical Hg
demethylation process derived from a magnetic isotope effect. Thus,
the Mass Independent Fractionation signature found in the hair of
volunteers was acquired before the methylmercury was incorporated
into the food web. A significant trend was found between δ202Hg and
Δ199Hg in the individuals from Pueblo Bello. Given that the obtained
Δ199Hg/δ202Hg slope (0.917±0.222; 2SE, n=36) was very low
compared to theoretical photodemethylation trends (a slope of
2.43±0.10, 1 SE), it was concluded that the observed tendency is most
likely produced by binary mixing, and is not related solely to a
photochemical process. Despite the fact that fish is not their only
protein source, the highest Δ199Hg values corresponded to people who
consumed mainly canned fish (especially sardines and tuna) and
fresh marine fish species. According to δ202Hg (range: +1.08 to
+2.46‰) and Δ199Hg (range: -0.01 to +0.57 ‰) signatures of the hair
samples from Puerto Nariño (Amazon), it was possible to determine
that this population is remarkably homogeneous, with similar sources
of Hg exposure. Since hair Δ199Hg values of the Amazon inhabitants
are close to 0, these were much lower than those of the Sierra Nevada
de Santa Marta inhabitants, but similar to the signature of Hg ores,
which highlights the influence of the gold mining activities carried out
in the region.
Finally, in the fourth project, the concentrations of eight essential
elements [Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co),
Nickel (Ni), Copper (Cu), Zinc (Zn), and Se] and four elements of
toxicological concern [Arsenic (As), Cd, Hg, and Lead (Pb)] were
determined in selected brands of canned sardines and tuna marketed
in Latin America and commercially available in the Amazon, with the
aim of estimating risk-based fish consumption limits. The Hg content
found during this study was much higher than that observed in
previous surveys carried out by our research group. According to the
Hazard Quotients obtained, all brands may present some risk in terms
of this element; especially brand F, in which levels up to 3.1 µg/g
were measured. Similarly, sardine samples surpassed the reference
limits of Mn and As. According to the observed trend, we highly
encourage the use of stricter quality control measures in retail chains
by industries, in order to guarantee safe levels of these elements in
fishery products.
LEER