The problem of contamination of Lerma River in the State of Mexico, México, has been studied in an integral way, since it is one of the rivers of importance due to its geographical situation in the country. José Antonio Dam is the main receiving body of this river that is being contaminated by, industrial wastewater, of which about 70% is inorganic, as well as discharges municipal and agricultural, driving a lot of material in suspension. This dam acts as a regulator of avenues and its water is used for agricultural irrigation and its sediments are used as sludge to improve agricultural soil in the surroundings. One of the studies that have been carried out is to determine the geochemical distribution of heavy metals in the sediments of this dam, as well as its adsorptive capacity towards different metals. It has been observed that these sediments acts as metal contaminants sequester. Knowing the composition and morphology of these sediments can provide information to understand the mobility of different heavy metals it contains, and potential health risk, which can finally lead to the establishment of purification capacity of this sludge.
It has been observed that natural processes for the formation of aquatic sediments are altered by human activities and are recognized as a reservoir for different chemical species, including metals [
Considering that sediments are complex systems where each metal has affinity to one or more of its components. The procedure of sequential extractions (chemical speciation) using chemical extractors to separate part of a metal associated with a component of the sediment, this technique has been successfully used for sediment characterization; the method most used to estimate the metallic reactivity in several types of particles enriched with adsorbed metals, has been developed since its inception by Tessier et al. in Canada [
• (F1), first extracted fraction called “Interchangeable” [
• (F2), fraction called “Acid-Soluble” [
• (F3) and (F4), fractions called “Easily Reducible” and “Hardly Reducible” respectively, contains the highest percentage of metals sequestered between nodules or cemented particles, in the first case, related to oxyhydroxides of Mn and in the second case related to oxyhydroxides of Fe; they are thermodynamically unstable under anoxic conditions and low reduction potentials [
• (F5), fraction denominated “Oxidable” in which metals are linked to different forms of organic matter; under oxidizing conditions organic matter is transformed and released metals which are forming soluble salts.
• (F6), fraction “Residual” or fixed is the one that can to hold back metals in its crystalline network.
On the other hand, considering the location area where this study was developed, it is necessary to indicate that, The Toluca Valley is located in Mexico State, México, has an important agricultural production and an accelerated urban-industrial growth, presents the problem that its aquifers are being overexploited and at the same time contaminating to Lerma River, main river of the zone, by to discharge of urban wastewater and of industrial discharges located in the industrial zone “Toluca-Lerma”, since it is one of the rivers of importance due to its geographical situation in the country. This river belongs to the Upper Basin of the Lerma River that starts in lagoons of Almoloya del Río with the concurrence of different tributaries, receiving the first discharges of wastewater between three and five kilometers, from its birth; continuing its trajectory and between ten and twelve kilometers it receives important discharges of wastewater, since in this section waters converge and coming from urban-industrial zone of Santiago Tianguistenco and its industrial parks I and II, Santa Cruz Atizapán and Ocoyoacac, which is the urban-industrial zone Toluca-Lerma, the municipal wastewater contributions of San Mateo Atenco, Metepec and the town of Lerma itself. The Lerma River crosses five states and finally discharges into Lake Chapala. Both the anthropogenic turns and the climate change have altered the sanitary conditions of the river throughout its journey, seriously affecting the biota that has already been extinct and especially the Lake Chapala. José Antonio Alzate Dam is the main receiving body of this river, was built in 1965 for flood control and agricultural irrigation, currently is being contaminated by, industrial wastewater, of which about 70% is inorganic, as well as discharges municipal and agricultural, driving a lot of material in suspension [
Among the anthropogenic waste discharged into the river, are the heavy metals that affect the José Antonio Alzate dam, this reservoir allows a work to purify the waters of the Lerma River and tributaries, although it has not been designed to it [
Metal | MOE criterion | Thomas-Mudroch criterion | EPA criterion for severe contamination |
---|---|---|---|
Cadmium | 1 | 1.5 | 6 |
Copper | 25 | 45 | 50 |
Iron | 10,000 | 45,500 | 25,000 |
Manganese | - | 1 625 | 500 |
Lead | 50 | 50 | 60 |
Zinc | 100 | 105 | 200 |
Three important areas of the Alzate dam were studied, which were called A, B, and F; where A is the entrance of Lerma river to the dam, therefore of alluvial carries and of agro-industry material; B zone is of greater sedimentation, according to Barceló, 2000; [
The drying of a part of the each sediment was completed by lyophilization, ground and sieved using US sieves. Tyler 60, 100, 250, 325 and 400 mesh, for the analysis of X-Ray Fluorescence (FRX), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), granulometry and determination of organic matter, the sediment retained in 100 mesh was used. Sediment retained to 400 meshes was used for chemical speciation studies. For total metals the weighted sum of each fraction of chemical speciation was used. For Textural and Granulometric classification of sediment, Bouyoucos hydrometric method and texture triangle were used. The volatile material determination was through weight loss, 1 g of sediment was heated in a Thermolyne 53,600 muffle for 3 hours at 150˚C, 300˚C and 500˚C, residual material was weighed after each stage. The weight of material removed in each sample for different temperatures was calculated by difference, all operations were carried out in triplicate.
Each concentration was determined using technique of sequential extractions for obtain the geochemical distribution of each metal (speciation) in sediment of three zones of the dam. Six fractions were obtained using chemical extractors in each case [
Sequential extractions technique by lyophilization was selected following the Quecholac methodology, where metals such as Cu, Fe, Mn among others were evaluated in their thesis work [
Metal | Total mg/kg | Total fractions continuous method mg/kg | Total fractions lyophilization method mg/kg | % mistake continuous method | % mistake lyophilization method |
---|---|---|---|---|---|
Cu | 50.04 | 54.142 | 48.875 | 8.19 | 2.32 |
Fe | 35547.70 | 46825.64 | 37516.73 | 31.72 | 5.54 |
Mn | 208.71 | 220.64 | 205.86 | 5.72 | 1.37 |
Based on the criteria indicated in
To classify the granulometry and texture of sediments, triangle of textures and the Bouyoucos technique were used respectively; the sediment composition of each area from Alzate dam is presented in % of distribution. Zone A presented the highest % of silt, classified as sandy-loamy (Cr); the other two were classified as clayey (R).
In
Zone A | Zone B | Zone F |
---|---|---|
Feldspar | Feldspar | Feldspar |
Hydrated Halloysite | Hydrated Halloysite | Hydrated Halloysite |
Meta Halloysite | Meta Halloysite | Meta Halloysite |
Cristobalite | Cristobalite | Cristobalite |
Chlorite | Mica | Chlorite |
Illite | Kaolinite | Tridimite |
- | Dickite | Dickite |
Amphibol | Amphibol | Amphibol |
Hematite (Fe2O3) | Hematite (Fe2O3) | Hematite (Fe2O3) |
Goethite (FeO∙OH) | Goethite (FeO∙OH) | - |
Metals Cd, Cu, Fe, Mn, Pb and Zn were evaluated in sediment of three zones of The J. A. Alzate Dam through of chemical speciation and total concentrations, considering criteria MOE, Thomas-Murdoch and EPA.
Cadmium was concentrated in greater proportion infractions F6, F4, F2 and F3 respectively (
In
Metal mg/kg | MOE criterion | Thomas-Mudroch criterion | EPA Criterion for severe contamination |
---|---|---|---|
Cadmium (Cd) | 1.00 | 1.50 | 6.00 |
Site | Considering the six fractions | Without considering F6 fraction | |
A | 5.51 | 5.51 | |
B | 9.39 | 9.39 | |
F | 4.82 | 4.82 |
In general, in sediments and soils [
Most of coppers are found in this fraction. One property of Cu2+ is its reduced mobility.
Metal mg/kg | MOE criterion | Thomas-Mudroch criterion | EPA Criterion for severe contamination |
---|---|---|---|
Cooper (Cd) | 25 | 45 | 50 |
Site | Considering the six fractions | Without considering F6 fraction | |
A | 44.45 | 32.30 | |
B | 50.14 | 36.03 | |
F | 30.75 | 19.75 |
For Thomas-Mudroch criterion, zones B and F exceeded the criterion and zone A is at the limit. For EPA criterion, zones A and F did not exceed this criterion and zone B is at the limit. In second case (five fractions) for the MOE criterion only zone F did not exceed the limit value, for Thomas-Mudroch and EPA criteria none of the three zones exceeded the limits. If MOE criterion is considered, the sediments of the three zones present contamination by copper; in this case it can also be a risk to aquifer health [
In crystallographic study the iron was found as oxide (Fe2O3) and as goethite (FeOOH), where this colloid has an adsorptive surface, it is possible that it is located in the extensive amorphous phase particularly as oxyhydroxides impregnated in clay minerals, kaolinite and quartz, which allows it to sequester metals as Cd, Cu, Pb and Zn.
Considering the criteria already described,
Metal mg/kg | MOE criterion | Thomas-Mudroch criterion | EPA Criterion for severe contamination |
---|---|---|---|
Iron (Fe) | 10,000 | 45,500 | 25,000 |
Site | Considering the six fractions | Without considering F6 fraction | |
A | 44620.51 | 27542.87 | |
B | 57152.38 | 35854.05 | |
F | 30559.42 | 18424.80 |
Metal mg/kg | MOE criterion | Thomas-Mudroch criterion | EPA Criterion for severe contamination |
---|---|---|---|
Manganese (Mn) | - | 1625 | 500 |
Site | Considering the six fractions | Without considering F6 fraction | |
A | 432.51 | 299.86 | |
B | 497.87 | 352.63 | |
F | 358.51 | 239.89 |
In speciation diagram (
Lead presence in sediments is due to the anthropogenic contributions of this metal, coming from industrial wastewater that Lerma River transports. According to chemical speciation results, this metal tends to concentrate towards the fractions with less mobility. Lead accumulation infractions F3, F4, F5 and F6, where the chemical mobility decreases respectively, leads to think that sediments work as traps for this metal, which means a decrease in the probability that it will be easily released to aqueous phase.
Metal mg/kg | MOE criterion | Thomas-Mudroch criterion | EPA Criterion for severe contamination |
---|---|---|---|
Lead (Pb) | 50 | 50 | 60 |
Site | Considering the six fractions | Without considering F6 fraction | |
A | 54.66 | 34.61 | |
B | 30.59 | 22.57 | |
F | 25.71 | 17.52 |
In the case of the five fractions (elimination of fraction F6), none of the three criteria was exceeded in any of the three zones. Lead was accumulated in higher concentration in F6 and because this fraction is totally immobile, its elimination is important since the values, when are compared with the three criteria, allow to evaluate each area as not contaminated by lead. It is important to be careful with this metal especially for the Daphnia pulex that can absorb it and bioaccumulate as it takes its food from sediments, being that this crustacean is an important food for the fish. It is necessary bear in mind that these metals type in biota generates a series of metabolic, physiological, behavioral and ecological effects [
Metal mg/kg | MOE criterion | Thomas-Mudroch criterion | EPA Criterion for severe contamination |
---|---|---|---|
Zinc (Zn) | 100 | 105 | 200 |
Site | Considering the six fractions | Without considering F6 fraction | |
A | 177.28 | 93.97 | |
B | 144.28 | 77.28 | |
F | 111.42 | 49.56 |
Despite of Zn is a metal required by organisms, an increase in concentrations makes it toxic to aquatic organisms. In the aquatic environment, Zn is mainly associated with suspended matter before accumulating in the sediment [
In so far as the texture and granulometry of the sediment, it was observed that sediments in zones B and F, that correspond practically to the dam, predominate clays, while in zone A, corresponding to the channel of the Lerma river. Silt was found in greater proportion, although it also drags clay and sand. Considering composition, feldspars and halloysite were found in the three zones. It is important to mention the goethite presence, because it has an important adsorption surface for metals, in addition to amorphous organic matter, where humic material presence also functions as adsorbent surface. These surfaces combined with clays are main materials like trap metals, as observed in geochemical Cd and Zn distribution, which was the most mobile metals since it was found more associated with carbonates (Fraction F2) and oxides as Fe and Mn, where surface goethite is probably the main surface (Fraction F4). In Cu case, the affinity for organic matter and sulfides is very noticeable (Fraction 5), although it was also concentrated in fraction F4 related to iron oxides. Pb presented a strong association with colloids of Mn, Fe, organic matter and sulphides in almost the same proportions (F3, F4 and F5 respectively) and very little relation with components of F1 and F2 fractions opposite of Cd. Concentration elevated for Cd and Pb was found in residual fraction F6. More elevated copper concentration was more accumulated in components of fraction F5. It was observed with respect to fraction F6 that zone B in general had the highest accumulation of all five metals. The association of these metals to sediment does not imply their total immobilization, since on the one hand, fine solid particles can be dragged towards other points of the reservoir, in which the physicochemical characteristics (including the pH and water aggressiveness) are different propitiating the re-dissolution of more labile or more mobile fractions (singularly for Cd). Regarding Fe and Mn, as indicated in sediment characterization analysis, the origin is basically geological. In case of Fe, it present as goethite (FeO∙OH) and Mn as manganite (MnOOH) are surface that can act as an adsorption surface for Cd, Cu, Pb and Zn, and that is, as sequestrants of these metals.
Finally, when the three criteria are compared, considering six fractions and first five, cadmium in the three zones exceed the limits of Canadian criteria, so it can be considered a pollutant for the sediment. In copper case, the MOE criterion limit was exceeded, considering only this criterion. The sediment is contaminated by copper. For Pb in none of the cases where the limits of these criteria exceed, at least in this study, is not considered the sediments contaminated by Pb in any of the three zones. It is important to consider better the first five fractions that are most mobile and present the risk of moving to aqueous phase, but not fraction F6 that is practically immobile, since metals are trapped in crystalline networks and are able to determine them whether it is necessary to use very acid digestions.
Knowing the composition and morphology of these sediments can provide information to understand the mobility of different heavy metals it contains and potential health risk which can lead to the establishment of its purification capacity. Considering everything discussed in this article, studying the sediment plays an important role in water bodies. It’s important conclude like many authors in this research field, that analytical measurements for specific total metal in an environmental and biological systems are insufficient. Among the most important metal speciation analysis is the assessment of the index of toxicity impacts of one specific metal and determination of ecological risk∙∙∙ Speciation analysis is an also analytical tool particularly used for the elucidation of the chemical form(s) as well as the quantitative estimation of a specific element when conducting toxicological and biochemical investigations [
Barceló-Quintal, I.D., Solís-Correa, H.E., García-Albortante, J., García-Martínez, M. and Jesús, L. Osornio-Berthet (2018) Behavior of Surface Sediment from the José Antonio Alzate Dam in Mexico as a Deposit of Heavy Metals. Journal of Environmental Protection, 9, 1049-1065. https://doi.org/10.4236/jep.2018.910065