Sources, Mobility And Bioavailability Of Metals And Metalloids In The Historically Mining And Smelter Impacted Altiplanean City Of Oruro, Bolivia (Chapter 1)

Chapter 1

Contamination in natural aqueous reservoirs: from general to specic observations

Contamination in natural aqueous reservoirs
1.1 Geochemistry in environmental sciences and environmental legislation: basic concepts
1.1.1 Introduction
During the 50s, the search for economically exploitable metallic deposits gave rise to the development of new techniques to nd cover deposits.Among these techniques, exploration With

geochemistry was a valuable tool to increase the discovery of these kind of deposits.

time, exploration geochemistry involved the generation of a vast terminology, in which terms such as: geochemical background, threshold, geochemical baseline, anomaly, enrichment factor, among others, are commonly. Nowadays these terms are mainly applied incontamination

and/or pollution studies, environmental sciences and environmental legislation, and regarding the last point, most of them are employed to assess the anthropogenic component in dierent environments of the Earth. Some authors have demonstrated that geochemical backgrounds, baselines, thresholds and anomalies depend on the location (e.g., [1, 2, 3]), scale and analytical techniques used(e.g., [4]). The following paragraphs will introduce the most important concepts applied in environmental geochemistry surveys and the meaning of geochemical studies to assess the degree of contamination

1

and/or pollution

2

in the environment.

1.1.1.1

Geochemical concepts applied to environmental sciences and environmental legislation

The term

geochemical backgroundcomes originally from exploration geochemistry.

It

was dened by Hawkes & Webb (1962) [5] as:  the normal abundance of an element in barren earth material and these authors concluded that  it is more realistic to view background as a range rather than an absolute value . The concept of geochemical background was introduced to dierentiate between normal element concentrations andanomalies , which might be indicative

of an ore occurrence.  By denition, an anomaly is a deviation from the norm. A geochemical anomaly, more specically, is a departure from the geochemical patterns that are normal for a given area or geochemical landscape [5]. and anomaly, the term To be able to dierentiate between background

threshold

was introduced and it was dened as  the upperlimit of

eects. All pollution is contamination, but not all contamination is pollution.
2

1 Make (something) impure by exposure to or addition of a poisonous or polluting substance. 2 The presence in or introduction into the environment of a substance or thing that has harmful or poisonous

Tapia et al.
normal background uctuation . A more general denition is that proposed by Garrett(1991) [6] as  threshold is the outer limit of background variation . Another term frequently used in environmental legislation is

geochemical baseline .

It was ocially introduced in the context

of the International Geological Correlation Programme (IGCP, projects 259 and 360; [7]) in order to create a global reference network for national regional geochemical data sets and as aninternational background database for environmental legislation. This term refers to the

prevailing variation in the concentration of an element in the supercial environment [8, 9] and furthermore, indicates the actual content of an element at a given point in time [9]; it includes the

natural background

and the diuse anthropogenic contribution in the soils [1, 10], in

which naturalbackground is widely used to infer background levels reecting natural processes uninuenced by human activities. This is an important issue (e.g., [7, 11]); however, Reimann & Garrett (2005) [4] believe that  the use of the term baseline gives the impression that there is a single number, line, where in fact there are a range of values characterizing any particular area or region reecting the...