**5. Conclusions**

a synergistic effect has been observed between SA and their potentiator. The toxicity effect of mixtures is associated with the transportation of toxic effects of individual chemicals into cells, the interaction toxic effects of individual chemical-binding-receptor proteins. According to

**Figure 3. (A)***D. magna* immobilization test: 48 h EC50 isobolograms of SMZ paired with other SAs and TMP at three selected combination ratios; **(B)** isobolograms of paired SQO and SGD *in D. magna* immobilization test (adopted from

References [25-26])

78 Organic Pollutants - Monitoring, Risk and Treatment

The reason for concern regarding risks of mixtures is obvious. Man is always exposed to more than one chemical at a time. This dictates the necessity of exposure assessment, hazard identification, and risk assessment of chemical mixtures. However, for most chemical mixtures data on exposure and toxicity are fragmentary, and roughly over 95% of the resources in toxicology is still devoted to studies of single chemicals. Moreover, organisms are typically exposed to mixtures of chemicals over long periods of time; thus, chronic mixture toxicity analysis is the best way to perform risk assessment in regards to organisms.

However, testing of all kinds of (complex) mixtures of chemicals existing in the real world or of all possiblecombinationsofchemicalsofasimple(defined)mixtureatdifferentdoselevelsisvirtually impossible. Moreover, even if toxicity data on individual compounds are available, we are still facing the immense problem of extrapolation of findings obtained at relatively high exposure concentration in laboratory animals to man being exposed to (much) lower concentrations.

As stated by several authors, it is essential to investigate if mixtures of pharmaceuticals interact, leading to a larger effect in the environment than would be predicted when each compound is considered individually. Mixtures with antibiotics in the environment may be very complex (e.g. wastewater effluent) but they also may be simple. Although the latter may be more easily studied experimentally, in both cases the identification and quantitative description of synergism caused by specific substances is crucial.

Over past 10 years there has been increasing interest in the impacts of SAs and other veterinary medicinesintheenvironmentandthereisnowamuchbetterunderstandingabouttheirenviron‐ mental fate and their impacts on aquatic and terrestrial organisms. However, there are still a number of uncertainties that require addressing before there can be a full understanding of the environmental risks of these compounds. Areas requiring further research are presented below. **•** The assessment of the potential impacts of those SAs for which ecotoxicity data is lacking but are seen to regularly occur in the environment.

**Abbreviation Full name**

PMT Pyrimethamine

RQ Risk Quotient SAs Sulfonamides SCP Sulfachloropyridazine SDM Sulfadimethoxine SDMD (SMZ) Sulfadimidine (Sulfamethazine) SDZ Sulfadiazine SGD Sulfaguanidine SMP Sulfamethoxypyridazine SMR Sulfamerazine SMTZ Sulfamethiazole SMX Sulfamethoxazole SPY Sulfapyridine SQO Sulfaquinoxaline SSX Sulfisoxazole STZ Sulfathiazole TMP Trimethoprim

**Table 5.** List of abbreviations used in the text

**Acknowledgements**

(2012-2015).

**Author details**

Gdańsk, Poland

PEC Predicted Environmental Concentration

What Do We Know About the Chronic and Mixture Toxicity of the Residues of Sulfonamides in the Environment?

http://dx.doi.org/10.5772/53732

81

PNEC Predicted Non-Effective Concentrations

Financial support was provided by the Polish National Science Centre under grant DEC-2011/03/B/NZ8/03009 "Determining the potential effects of pharmaceuticals in the environment: an ecotoxicity evaluation of selected veterinary drugs and their mixtures"

Department of Environmental Analysis, Faculty of Chemistry, University of Gdańsk,

Anna Białk-Bielińska, Jolanta Kumirska and Piotr Stepnowski

