**2. The potential ecological risk index**

#### **2.1 Theoretical hypothesis**

Considering the different aspects that could affect ecological risk, Håkanson [7] made four hypotheses about the potential ecological risk index (ERI) value when he proposed the approach. They are:


#### **2.2 Equations**

Based on the above hypothesis, the potential ecological risk index is calculated by the following equations:

$$\mathbf{C}\_{f}^{i} = \frac{\mathbf{C}\_{0-1}^{i}}{\mathbf{C}\_{n}^{i}} \tag{1}$$

$$\mathbf{C}\_d = \sum\_{i=1}^n \mathbf{C}\_f^i = \sum\_{i=1}^n \frac{\mathbf{C}\_{0-1}^i}{\mathbf{C}\_n^i} \tag{2}$$

*Water Quality Ecological Risk Assessment with Sedimentological Approach DOI: http://dx.doi.org/10.5772/intechopen.88594*

where *C<sup>i</sup> <sup>f</sup>* is the contamination factor of the substance i, *Ci* <sup>0</sup>�<sup>1</sup> is the measured value of the substance i, *C<sup>i</sup> <sup>n</sup>* is the preindustrial reference value of the substance i, and *Cd* is the degree of contamination.

$$E\_r^i = T\_r^i \cdot \mathbf{C}\_f^i \tag{3}$$

$$ERI = \sum\_{i=1}^{n} E\_r^i = \sum\_{i=1}^{n} T\_r^i \cdot C\_f^i \tag{4}$$

where *Ei <sup>r</sup>* is the potential ecological risk factor for the given substance i, *T<sup>i</sup> <sup>r</sup>* is the "toxic-response" factor for the given substance i, and ERI is the potential ecological risk index for the basin/lake.

#### **2.3 The parameters**

the background value, and the background matrix correction factor of lithogenic effects is considered in it [4]. The pollution load index (PLI) is defined as the nth root of the product of the ratios between the concentration of each metal to the background values [5]. The sediment quality guidelines (SQGs) include threshold effect concentrations (TECs) and probable effect concentrations (PECs). Bioavailability is taken into account in this approach [6]. It is not adequate to assess the ecological risk by using only concentrations without factors of toxicity. The potential ecological risk index (ERI) posed by Swedish geochemist Lars Håkanson (The National Swedish Environment Protection Board, Water Quality Laboratory Uppsala) is based on the "abundance principle", "sink-effect", and "sensitivity factor" [7]. As a diagnostic tool for pollution control, the potential ecological risk index has

This chapter describes an approach to assess water quality risks using its basic theory, calculation formula, evaluation criteria, and parameters calculation. This approach combines environmental chemistry with ecotoxicology in order to assess the potential risks accurately. The approach integrates the concentration of substances with ecological effects, environmental effects, and toxicity. Furthermore, the model is used to explain in detail a water quality case study of the Liaohe River,

Considering the different aspects that could affect ecological risk, Håkanson [7] made four hypotheses about the potential ecological risk index (ERI) value when he

1.The concentration requirement. The ERI value should increase as the pollutant

2.The number requirement. The ERI value should increase as the number of

3.The toxic factor requirement. Various substances have different toxicological effects. ERI value should differentiate between mildly, moderately and very

4.The sensitivity requirement. Various lakes and water systems do not have the

Based on the above hypothesis, the potential ecological risk index is calculated

*Ci* 0�1 *Ci n*

(1)

(2)

*Ci <sup>f</sup>* <sup>¼</sup> *<sup>C</sup><sup>i</sup>* 0�1 *Ci n*

*Cd* <sup>¼</sup> <sup>X</sup>*<sup>n</sup> i*¼1 *Ci <sup>f</sup>* <sup>¼</sup> <sup>X</sup>*<sup>n</sup> i*¼1

been widely used since its development in the 1980s [8–10].

**2. The potential ecological risk index**

*Water Quality - Science, Assessments and Policy*

**2.1 Theoretical hypothesis**

proposed the approach. They are:

contamination increases.

pollutant species increase.

same sensitivity to toxic substances.

toxic substances.

by the following equations:

**2.2 Equations**

**72**

China [11].

#### *2.3.1 The contamination factor C<sup>i</sup> f*

To get the value of the contamination factor (*C <sup>i</sup> <sup>f</sup>* Þ, more information needs to be known about the measured value of substance i (*C<sup>i</sup>* <sup>0</sup>�1) and the preindustrial reference value of substance i (*C<sup>i</sup> <sup>n</sup>*). In order to reflect the risk of the lake accurately, Håkanson proposed that "undisturbed" samples should be collected from accumulation areas in the lake targeting the 0–1 cm layer. Håkanson provides two methods to determine the accumulation areas for a given lake. The first method, the ETAdiagram (**Figure 1**), uses only the water depth and the effective fetch. The second method uses the water content of sediments (*W*<sup>0</sup>�1). In this second method, researchers have to collect and analyze sediments to determine the bottom dynamic condition. The method requires 5 g wet sediment dried for 6 h at 105°C, then expressed as the water content as wet sediment. Accordingly, if the *W*<sup>0</sup>�<sup>1</sup>>75%, it may mean the sediments are from an accumulation area.

In addition, Håkanson gives the types of contaminants that could be included in this contamination factor index. These contaminants include PCB, Hg, Cd, As, Cu, Pb, Cr, and Zn. Of course, it is possible to study other pollutants

**Figure 1.** *The ETA-diagram [12].*

(e.g., Ni, V, Mo, Co). Fe, Mn, and P are unsuitable as sediment parameters in this approach because their concentration is often influenced by physical or chemical processes in the sediments.

According to the contamination factor (*C <sup>i</sup> <sup>f</sup>* ), single elements, *C <sup>i</sup> <sup>f</sup>* are classified as follows:

*C i <sup>f</sup>* <1, low contamination factor; 1≤ *C <sup>i</sup> <sup>f</sup>* <3, moderate contamination factor; 3≤ *C <sup>i</sup> <sup>f</sup>* <6, considerable contamination factor; *C i <sup>f</sup>* ≥6, very high contamination factor.

For the preindustrial reference condition *C<sup>i</sup> n* ), Håkanson chose preindustrial background reference values as PCB = 0.01, Hg = 0.25, Cd = 1.0, As = 15, Cu = 50, Pb = 70, Cr = 90, and Zn = 175 (ppm). Different researchers [13–15] have selected other reference values for *C<sup>i</sup> n*, for example, the national standards and the background reference value.
