**2.2 Selection of sampling sites**

The selection of the ten sampling points was representative of the system, both in number and location. Given the influence of seasonal variability [2]. A standardized collection study was performed; that is the entire study area during a similar period at the same depth, of a similar substrate [21]. Samples (sediment and water) were taken according to standardized methods [22].

#### **Figure 1.** *The geographical location of the City of Carmen and "Terminos" lagoon.*

*Quantification of Heavy Metal Levels in Sediments of the "Palizada" River in a Protected… DOI: http://dx.doi.org/10.5772/intechopen.104657*

#### **Figure 2.**

*The geographical location of the "Palizada" river.*


#### **Table 1.**

*Sediment sampling points of the "Palizada" river.*

### **2.3 Sample treatment**

#### *2.3.1 Treatment of glassware and preparation of standards*

The glassware was treated with a 10% nitric acid (HNO3) mixture, as suggested by US-EPA method 3050B [23], and dried at a temperature of 105°C for later use. Calibration standards for Cu, Pb, Cd, Fe, Mg, and Mn (**Table 2**), at 50 or 100 mL, were prepared. The calibration blank was a 5% solution of HNO3.


**Table 2.**

*Working ranges and wavelengths (α), used in the analysis of heavy metals.*

#### *2.3.2 Sediment sample treatment for heavy metal analysis*

The sediment samples were dried at a temperature of 105°C for 24 hours, later they were treated in digestion with nitric acid (HNO3), hydrochloric acid (HCl), and hydrogen peroxide (H2O2) [23]. The resulting solution is filtered, and deionized water is added to it up to 100 mL, as suggested by EPA method 3050B [23]. The equipment used for the analysis was an atomic absorption spectrum Mark Thermo Scientific, the model is ICE 3500.

### *2.3.3 Sediment texture and Organic Matter (OM)*

Granulometry analyses were carried out using the hydrometer of the Bouyocos Technique [24], OM was analyzed by the method suggested in NMX-AA-034- SCFI-2001 [25]; The principle of this method is based on the quantitative measurement of OM contained in water by evaporation and calcination of the samples and is summarized by the following steps: the dry sediment sample, previously pulverized, is sieved to obtain a specific particle size. This method requires constant weight measurements of porcelain vessels (crucibles), and sample calcination at 550°C to measure organic matter by weight difference with the following Eq. (1):

$$\text{MO} = \left(\text{GI} - \text{G}\right) \* \text{1} \odot \text{O} \tag{1}$$

Where:

OM: organic matter in mg/L

GI: is the weight of the crucible with the sample, before calcination (mg) G: is the total weight of the crucible with the sample after calcination, in mg

## **2.4 Statistical analysis**

To determine the variations by climatic season and by site, a one-way analysis of variance (ANOVA) was used. To establish the relationships between sediment texture, OM, and heavy metals, a Pearson correlation and multiple correlations (Software: Statistical 7.1) were used [26]. The normality of the data was verified using the Shapiro-Wilks statistical test (Software: Statistical 7.1).

*Quantification of Heavy Metal Levels in Sediments of the "Palizada" River in a Protected… DOI: http://dx.doi.org/10.5772/intechopen.104657*
