Bioassays in contaminant analysis

Hoogenboom, State Institute for Quality Control of Agricultural Products (RIKILT), Wageningen 

However, despite the rapid improvements in analytical chemistry, at the same time we start to realize that these methods may no longer be sufficient to deal with the often very complex mixtures of chemicals or ever changing chemical structures of toxicants present as residues in our food chain. Furthermore, there is a strong need for rapid screening assays that can be used for extensive monitoring programmes. 

Bioassays with pro- or eukaryotic cells capable of detecting compounds based on their effects, offer a possible solution. For the detection of antibiotics in milk and meat, a number of different tests are used for the screening4 5 and in many cases, chemical identification of the responsible substances is no longer required. Recent advances in cell biology and in particular biotechnology have 

Several other dioxin and PCB congeners have been tested and were shown to give a response that reflects the differences in the TEF values (Fig. 5.3). However, congeners with a low TEF value showed a relatively low response in the test. This is similary true for 1,2,3,7,8-PeCDD which TEF value was recently adjusted from 0.5 to 1, and which is often a relatively important contributor to the total dioxin content. As a result the test may underestimate the total TEQ content, if calculations were based on the calibration curve for TCDD. However, in general it is evident that the bioassay obeys the TEQ principle and that the result will reflect the total TEQ content of the sample. 

Following the succesful development of the cells, a rapid clean-up procedure for fat samples was developed, based on the use of an acid silica column. Using 

---

There is no doubt as to the remarkable potential of the EC-MS technique for the analysis of biotoxins it represents a serious alternative to the mouse bioassay or, at least, a supplementary analytical tool for tracing an extensive toxin profile of contaminated shellfish. The current rapid developments in EC-MS methodology look promising for a close attainment of these objects however, further improvement and interlaboratory studies will be necessary. In addition, a serious problem, which does not allow, at present, this technique from becoming a generally accepted tool in regulatory analysis is the nonavailability of pure analytical standards and reference materials for most YTXs. 

Ke, R. Li, J. Qiao, M. Xu, Y. Wang, Z. 2007. Using Semipermeable Membrane Devices, Bioassays, and Chemical Analysis for Evaluation of Bioavailable Polycyclic Aromatic Hydrocarbons in Water. Archives of Environmental Contamination and Toxicology, v.53, p.313-320. 

The sediment from Amerikahaven (site 10) was found to contain unexpectedly low contaminant levels during sampling in 1996 (see also De Boer et al., 2001). This was attributed to repeated dredging activity. The sediment was therefore sampled a second time in September 1997 at a non-dredged site. Analysis of this sediment showed considerably higher contaminant levels. These results are considered more representative of this location and were therefore used instead of the 1996 data in the multivariate statistical analysis of biomarker data. Sediment bioassays were however conducted with the material collected in 1996 and these data for location no. 10 were used for multivariate analysis when sediment chemistry was included. 

Bioassay procedures for the determination of gibberellic acid have been developed (2, 5), but more recent chemical fluorometric assay methods are equally specific. However, both assay methods show a low response with samples containing less than 10 /x/xg. of the gibberellins. Consequently, in determining residual amounts within the part per billion (p.p.b.) range, relatively large samples must be extracted and extracts partially purified to satisfy the assay conditions. These operations are usually accompanied by some material losses or degradation, which impair quantitative interpretation of the results. Natural inhibitors can influence the results in the bioassay method (2), and fluorescent contaminants can interfere with the spectrophotometric analysis. 

Methods to determine the potential biological activity of products obtained through recombinant DNA techniques are of fundamental importance. Despite the existence of numerous physicochemical techniques to characterize the protein product structure and the presence of contaminants, they provide little, if any, information about its biological potency. A bioassay is defined as a functional test, and no physicochemical test can measure the function. However, for some peptide hormones, which are less complex in structure than most cytokines, well defined physicochemical tests may be used to estimate biological activity for instance, the capillary electrophoresis analysis of a protein s isoform content if the specific activity of each one is known. 

In addition, the testing laboratory for both nutrients and unintentional contaminants, including carcinogens, may perform periodic analysis of the basal diet. The results of such analysis should be retained and included in the final report on each chemical. When the test chemical is administered in water or food, stability tests are essential. Properly conducted stability and homogeneity tests, prior to the chronic study, should be used to establish the frequency of diet preparation and monitoring required. When diets are sterilized, the effects of such procedures on the test chemical and dietary constituents should be known. Appropriate adjustments to nutrient levels should be performed. The effect of chemical sterilants, (e.g., ethylene oxide) on the bioassay should be ascertained. 

---