**1. Introduction**

For ten years now, interest has been increasing in research focused on pharmaceutical residues in the environment. Special attention has been given to the residues of antimicrobials, since it has been demonstrated, that due to the formation of the dangerous phenomenon of bacterial resistance, these substances could pose a real threat not just to ecosystems, but also to human health. Most antimicrobial agents are used in large quantities for different purposes in veterinary medicine.

Various antibiotics are commonly used in this field, but we shall concentrate on sulphonamides (SAs). The physicochemical properties and chemical structures of selected SAs are presented in Table 1.

Having been used for more than fifty years, SAs are among the oldest groups of veterinary chemotherapeutic substances. They are inexpensive and offer a broad spectrum of activity for the prevention and treatment of bacterial infections. After tetracyclines, they are the most commonly consumed veterinary antibiotics in the European Union [1,10]. However, as animals do not completely metabolize these compounds, a large fraction of them is being excreted unchanged in faeces and urine. Therefore, both the unmetabolized drugs and their metabolites are discharged to the environment, mainly to the soil component, either directly by grazing animals or indirectly during the application of manure [11]. Once in the soil, they and their transformation products are distributed among its different compartments and can be transported to the surface and ground waters. The physicochemical properties of these compounds, the applied dosage and the nature of the environmental compartment where they are released and further interact, comply the whole process.

© 2014 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.



**Substance [CAS] Abbreviation**

[80-32-0]

Sulphadiazine [68-35-9]

Sulphadimethoxine [122-11-2] SDM

Sulphadimidine (sulphamethazine)

Sulphaguanidine [57-67-0] SGD

Sulphamerazine [127-79-7]

Sulphamethoxazole

[723-46-6]

[57-68-1]

Sulphachloropyridazine

SCP <sup>2</sup>NH S

658 Environmental Risk Assessment of Soil Contamination

SDZ <sup>2</sup>NH <sup>S</sup>

SDMD (SMZ) <sup>2</sup>NH <sup>S</sup>

SMR <sup>2</sup>NH <sup>S</sup>

SMX <sup>2</sup>NH S

**Chemical structure Selected physicochemical properties**

Cl M = 284.7 g mol-1

N M = 250.3 g mol-1

N M = 278.3 g mol-1

N M = 264.3 g mol-1

pKa2 = 1.72 pKa3 = 6.39 logP = 0.71

pKa2 = 1.98 pKa3 = 6.01 logP = -0.09

M = 310.3 g mol-1 pKa2 = 2.5 pKa3 = 6.0 logP = 1.63

> pKa2 = 2.46 pKa3 = 7.45 logP = 0.27

M = 214.2 g mol-1 pKa2 = 2.8 pKa3 = 12.0 logP = -1.22

> pKa2 = 2.16 pKa3 = 6.80 logP = 0.11

M = 253.3 g mol-1 pKa2 = 1.81 pKa3 = 5.46 logP = 0.89

O O

> O O HN N

NH

O O HN N

NH C

N O

O

O O HN N

> O O

HN

O

N N

OMe

OMe

NH

NH2

2NH S

<sup>2</sup>NH S

O

O

HN

N N

**Table 1.** The structures and physicochemical properties of the sulphonamides discussed in this chapter (according to [1-9])

SAs are fairly water-soluble, polar compounds, however quite persistent - resistant to biode‐ gradation [10,12-13] and hydrolysis [3]. This goes a long way to explaining why they have been regularly detected in both aquatic and terrestrial environments in the last ten years [1,10-11]. Although SA concentrations in environmental samples are relatively low (at the ppb or ppt level), they are continuously being released, so ultimately they may pose an elevated risk. SAs are designed to specifically target the biosynthetic pathway of folate (an essential molecule required by all living organisms) by competitively inhibiting the conversion of *p*-aminobenzoic acid (pABA); hence, they not only target bacteria but can also elicit hitherto unknown effects in environmentally relevant, non-target organisms like invertebrates and plants [14-16]. As they belong to different trophic levels, these taxonomic groups may be exposed to SAs to various extents.

So far only a small number of studies concerning the presence and effects of SAs in the soil environment have been carried out. Hence, there are a number of very pertinent questions that need to be addressed, for example: (i) What is the fate of these compounds in the terrestrial environment? (ii) What are the effects of their presence in the soil environment? (iii) Do they pose a risk to different soil organisms and also to human health?

For these reasons, the aim of this chapter is to review and summarize existing knowledge of the fate and effects of SA residues in the terrestrial environment.

Conventionally, the environmental fate of antimicrobials in the soil ecosystem is assessed with respect to their persistence and sorption onto soil. In the case of SAs, as they are very stable, only photodegradation process could have recognizable influence on their elimination from the environment [1,10]. However this process in the soil ecosystem is of lesser importance. Therefore, sorption processes influence the environmental behaviour of SAs to the greatest extent, so it is these that we shall be discussing in detail.

Although a few review papers have been published summarizing the available ecotoxicity data of pharmaceuticals, including some SAs [14-15,17-18], they focus on aquatic organisms rather than soil. In this chapter, therefore, we shall discuss the available data on SA toxicity towards different soil organisms on various trophic levels like bacteria, invertebrates and plants. These results will be discussed with respect to the existing requirements for the environmental risk assessment of veterinary pharmaceuticals (VICH, 2000 [19]; VICH, 2004 [20]; EMEA, 2007 [21]; EMEA, 2008a [22]; EMEA, 2008b [23]). In addition, we shall identify some areas where future work is warranted as well as the needs for further investigations.
