Lipids in preventive dentistry.

OBJECTIVES: There is still a great demand for the improvement of oral prophylaxis methods. One repeatedly described approach is rinsing with edible oils. The aim of the present review paper was to analyze the role of lipids in bioadhesion and preventive dentistry. MATERIALS AND METHODS: Despite limited sound scientific data, extensive literature search was performed to illustrate possible effects of lipids in the oral cavity. RESULTS: It is to be assumed that lipophilic components modulate the process of bioadhesion to the oral hard tissues as well as the composition and ultrastructure of the initial oral biofilm or the pellicle, respectively. Thereby, lipids could add hydrophobic characteristics to the tooth surface hampering bacterial colonization and eventually decreasing caries susceptibility. Also, a lipid-enriched pellicle might be more resistant in case of acid exposure and could therefore reduce the erosive mineral loss. Furthermore, anti-inflammatory effects on the oral soft tissues were described. However, there is only limited evidence for these beneficial impacts. Neither the lipid composition of saliva and pellicle nor the interactions of lipids with the initial oral biofilm and the pellicle layer have been investigated adequately until now. CONCLUSION: Edible oils might qualify as mild supplements to conventional strategies for the prevention of caries, erosion, and periodontal diseases but further research is necessary. CLINICAL RELEVANCE: Against the background of current scientific and empirical knowledge, edible oils might be used as oral hygiene supplements but a decisive benefit for the oral health status is questionable.

Effect of safflower oil on the protective properties of the in situ formed salivary pellicle.

AIM: The prevalence of dental erosion is still increasing. A possible preventive approach might be rinsing with edible oils to improve the protective properties of the pellicle layer. This was tested in the present in situ study using safflower oil. METHODS: Pellicle formation was carried out in situ on bovine enamel slabs fixed buccally to individual upper jaw splints (6 subjects). After 1 min of pellicle formation subjects rinsed with safflower oil for 10 min, subsequently the samples were exposed in the oral cavity for another 19 min. Enamel slabs without oral exposure and slabs exposed to the oral cavity for 30 min without any rinse served as controls. After pellicle formation in situ, slabs were incubated in HCl (pH 2; 2.3; 3) for 120 s, and kinetics of calcium and phosphate release were measured photometrically (arsenazo III, malachite green). Furthermore, the ultrastructure of the pellicles was evaluated by transmission electron microscopy (TEM). RESULTS: Pellicle alone reduced erosive calcium and phosphate release significantly at all pH values. Pellicle modification by safflower oil resulted in an enhanced calcium loss at all pH values and caused an enhanced phosphate loss at pH 2.3. TEM indicated scattered accumulation of lipid micelles and irregular vesicle-like structures attached to the oil-treated pellicle layer. Acid etching affected the ultrastructure of the pellicle irrespective of oil rinsing. CONCLUSION: The protective properties of the pellicle layer against extensive erosive attacks are limited and mainly determined by pH. The protective effects are modified and reduced by rinses with safflower oil.

The lipid composition of the in situ pellicle.

OBJECTIVE: The present study aimed to systematically analyse the complete lipid profile of the in situ pellicle in comparison to saliva. For the first time, the modern sensitive methods GC-EI/MS and HPLC MS/MS were to be used for this purpose. DESIGN: Bovine enamel slabs were exposed to the oral cavity of 12 subjects by customized splints (3 min, 30 min or 120 min). Afterwards, the pellicle samples were obtained and further investigated in vitro. Additionally, corresponding unstimulated saliva samples were collected. GC-EI/MS was performed to qualitatively and quantitatively determine all fatty acids contained in the investigated samples. The individual lipid classes of phospholipids, triacylglycerols, glycolipids, cholesterol and cholesterol esters were analysed qualitatively by HPLC MS/MS. RESULTS: A characteristic fatty acid profile of the in situ pellicle was proven. Furthermore, triacylglycerols with the major fatty acids 16:0, 18:0, 18:1, 18:2, and phospholipids were detected as integral components in the pellicle. There were four groups of phospholipids: Lyso-phosphatidylcholines, phosphatidylcholines, phosphatidylethanol-amines, and phosphatidylinositols. Differences between saliva and pellicle were evident in the composition of the fatty acid- and the phospholipid profile. Glycolipids, cholesterol and cholesterol esters could neither be detected in pellicle- nor in saliva samples. CONCLUSION: The lipid profiles of the in situ pellicle and saliva were successfully characterised. Differences in the phospholipid and fatty acid composition between pellicle and saliva indicate a selective pellicle formation process. The results provide an important reference and core data for further investigation of the complex surface interactions in the oral cavity, especially concerning hydrophobic substances.

The role of irradiation source setups and indirect phototransformation: Kinetic aspects and the formation of transformation products of weakly sunlight-absorbing pesticides.

In this study, emission spectra of three different commonly used xenon irradiation sources were analyzed and compared for the first time to ascertain the most suitable setup to simulate natural solar radiation. In order to demonstrate setup differences, absolute photon fluxes of irradiation sources were received by actinometry. Verification was done by measuring quantum yields of the model compounds Penconazole, Terbutryn, and Mecoprop in every setup. Differences regarding kinetic aspects and the formation of transformation products (TPs) was evaluated by analyzing direct phototransformation and additionally photolysis in presence of Nitrate as a photosensitizer in one irradiation setup (optical bench). Results showed that a precise setup characterization is needed to estimate whether irradiation sources are suitable to simulate terrestrial sunlight. This was found to be especially important for weakly sunlight-absorbing substances. In comparison with direct photolysis, indirect photolysis led to an enhancement of degradation rate constants for all substances and in case of Mecoprop to different types of TPs that were formed during irradiation. This study underlined that there are big knowledge gaps regarding irradiation sources setups and conditions. It is therefore absolutely necessary to consider those factors while simulating substance degradation and the TP formation under environmental conditions.

Photolysis of mixtures of UV filters octocrylene and ethylhexyl methoxycinnamate leads to formation of mixed transformation products and different kinetics.

The treatment with ultraviolet (UV) light is a well-known technique for water disinfection. Photodegradation by UV light is in discussion as measure for advanced water treatment that could provide a potential removal option for micropollutants. Micropollutants such as ingredients from personal care products are also present in grey water. Grey water gets increasingly attention as a source for water reuse. For that purpose it has to be treated. UV-treatment is an option. However, the knowledge on the fate of micropollutants within such a treatment is little. Therefore, we investigated the fate of the UV filters ethylhexyl methoxycinnamate (EHMC), and octocrylene (OCR) as for both UV filters the presence in grey water was reported. OCR as a single compound was investigated with regard to its degradation kinetics and possible photo-transformation products (photo-TPs). These results were compared with those of EHMC previously reported in literature. The mixture of the two UV filters was also investigated to reveal if mixture effects occur regarding the elimination of the UV filters and the formation of TPs. A medium pressure mercury vapor lamp (200-400 nm) was employed for photolysis. This study shows that OCR itself was eliminated below the limit of detection after 256 min and that photo-TPs were formed. The photolysis of the mixture demonstrated alterations of the degradation rates and patterns. Additional TPs were formed by the reaction of the UV filters or TPs with each other. The study shows that more attention should be paid to mixture-effects and mixture-TPs that may cause further follow-up effects.

Mixtures of quaternary ammonium compounds and anionic organic compounds in the aquatic environment: Elimination and biodegradability in the closed bottle test monitored by LC-MS/MS.

Quaternary ammonium compounds (QACs) are widely used as disinfectants, detergents and fabric softeners. Anionic detergents are one of the most widely used chemical substances. QACs and anionic surfactants can form ionic pairs. In the present study we investigated the biodegradability of QACs in the presence of different anionic surfactants. The biodegradability of three QACs, namely benzalkonium chloride (BAC), didecyldimethylammonium chloride (DDMAC) and ethacridine lactate (EL), when applied as single substances and in combination with anionic surfactants such as benzene sulfonic acid (BSA), LAS, naphthalene sulfonic acid (NSA) and sodium dodecylsulfonate (SDS) was studied applying the closed bottle test (CBT) [OECD 301D, 1992. Guidelines for Testing of Chemicals. Closed bottle test. Organisation of Economic Cooperation and Development, Paris] at a ratio of 1:1 (mol:mol). Biodegradation was monitored by measuring oxygen concentration in the test vessels with an oxygen electrode in accordance with international standard methods [ISO 5414, 1990. Water quality - determination of dissolved oxygen. In: German Standard Methods for the Examination of Water, Wastewater and Sludge. VCH Verlagsgesellschaft, Weinheim, New York, Basel Cambridge]. Primary elimination of the QACs and of LAS was monitored by LC-MS/MS. There was little biodegradability of the QACs as either single compounds or in the presence of organic counter ions. The biodegradability of the organic counter ions was lower in the presence of QACs as compared to the single substances. Primary elimination of the QACs by sorption took place.

The toxicity of the quaternary ammonium compound benzalkonium chloride alone and in mixtures with other anionic compounds to bacteria in test systems with Vibrio fischeri and Pseudomonas putida.

Mixtures of chemicals are present in the aquatic environment but standard testing methods assess only single compounds. One aspect of this question is the importance of the formation of ionic pairs, for example from quaternary ammonium compounds with organic anions, and the significance of the ionic pairs for bacterial toxicity in the aquatic environment. The aim of the present study was to investigate the toxicity of the cationic quaternary ammonium compound benzalkonium chloride (BAC) against aquatic bacteria in the presence of substances commonly found in wastewater, such as the anionic surfactant linear alkylbenzene sulfonate (LAS), naphthalene sulfonic acid (NSA), sodium dodecylsulfonate (SDS), and benzene sulfonic acid (BSA). The growth inhibition test with Pseudomonas putida and the Vibrio fischeri luminescent inhibition test were used to determine the toxicity of single compounds and compound mixtures. The results found in this study indicate that ion pair formation is of minor significance under the test conditions applied here.

Photodegradation of the UV filter ethylhexyl methoxycinnamate under ultraviolet light: Identification and in silico assessment of photo-transformation products in the context of grey water reuse.

To prevent water shortages in the future and to reduce domestic water consumption, decentralized grey water (GW) reuse has become increasingly important. This water has, however, to be free of pollutants. Conventional treatment of GW does not fully eliminate micropollutants such as the UV filter substance ethylhexyl methoxycinnamate (EHMC). EHMC, which is commonly used in sunscreens and personal care products, is an endocrine disruptor and shows potential to bioaccumulation, which is also reflected in its low water solubility. Photolysis has been proposed as an alternative treatment method for other micropollutants, but it is not clear yet whether it can also be used to eliminate EHMC. One goal of this study was to better understand the basic pathways involved in this process. It aimed to identify photo-transformation products (photo-TPs) by using, in the test conditions, an initial concentration of EHMC higher than those expected in the environment. Acetonitrile (ACN) was added in low concentrations to the aqueous solution to overcome the low aquatic solubility of EHMC. The influence of this co-solvent on the degradation kinetics was studied. The photolysis experiments were carried out using a medium pressure mercury lamp, which emits UV light in the range of 200-400nm. The quantum yield of the photolysis of EHMC was 0.0042 and 0.0023mol·Einstein-1 (for 0.2 and 0.5% ACN (v/v), respectively), and the relative and absolute UV photon fluxes were determined. HPLC was used to monitor the elimination kinetics of EHMC, which followed first-order kinetics. The results of LC-MSn analyses revealed that beside others, several oxidized and hydroxylized EHMC isomers were formed as photo-TPs in aqueous solution. Using a set of in silico quantitative structure-activity relationship (QSAR) models, this study also offered new insights concerning the environmental fate and toxicity of the TPs of EHMC.

Usage pattern-based exposure screening as a simple tool for the regional priority-setting in environmental risk assessment of veterinary antibiotics: a case study of north-western Germany.

Veterinary antibiotics (VAs) are widely recognized as important environmental contaminants. Despite the extensive use of antibiotic agents in meat and poultry production and the known resistance problems in human and veterinary medicine, detailed knowledge about usage patterns of VAs in Germany is still scarce. This lack of knowledge severely impacts current research on the environmental risk of VAs, but it is expected that recently established surveillance programs for antimicrobial drug usage will close this knowledge gap. Therefore, a spatially more precise environmental risk assessment and management might become possible in the near future. In this study, a new usage pattern-based exposure screening (UPES) approach for the comprehensive environmental exposure assessment of veterinary antibiotics was preliminarily assessed using approximated scenarios of antimicrobial substance usage in German meat and poultry production. Resulting predicted manure concentrations covered seven orders of magnitude ranging from ng kg(-1) to g kg(-1) dry weight (dw). Beyond that 14 antibiotic substances of 10 different antimicrobial classes were predicted to have the potential to occur in soil concentrations higher than 100 µg kg(-1) dw. These findings raise further questions regarding the environmental exposure and risks of frequently used VAs, especially in regions with higher-than-average livestock density. With this case study we demonstrate that UPES simplifies to account for differing local agricultural factors and therefore facilitates priority-setting on a regional level. In this context a simple prioritization scheme for environmental assessment of VAs, considering both the expected environmental concentration and the frequency of application, is proposed in this paper.

Physico-chemical characteristics affect the spatial distribution of pesticide and transformation product loss to an agricultural brook.

Diffuse entry of pesticide residues from agriculture into rivers is spatially unevenly distributed. Therefore, the identification of critical source areas (CSAs) may support water quality management in agricultural catchments. In contrast to former studies, we followed the hypothesis that not only hydrological and topographical characteristics but also physico-chemical properties of pesticide residues have a major influence on their loss to rivers and on corresponding formation of CSAs. We designed a virtual experiment, i.e. a numerical experiment as close as possible to environmental conditions, in a headwater catchment where pronounced spatial differences in hydrological transport processes were identified in the past. 144 scenarios with different combinations of adsorption coefficients (KOC = 10-1000 ml/g) and transformation half-lives (DT50 = 3-60 days) for pesticide parent compounds (PCs) and their transformation products (TPs) were simulated using the catchment-scale spatially distributed reactive transport model ZIN-AgriTra. Export fractions of substances in the virtual experiment ranged from 0.001-15% for pesticides and 0.001-1.8% for TPs. The results of the scenario investigations suggest that more of the calculated export mass variability could be attributed to KOC than to DT50 for both PCs and TPs. CSAs for TPs were spatially more equally distributed in the catchment than for PC export which was likely an effect of changing physico-chemical properties during transformation. The ranking of highest export fields was different between PCs and TPs for most of the investigated scenarios but six fields appeared among the top ten export fields in 95% of the scenarios, which shows the influence of site characteristics such as tile drains or soil properties in the catchment. Thus, the highest export fields were determined by a combination of site characteristics and substance characteristics. Therefore, despite the challenge of widely differing physico-chemical characteristics of pesticides on the market, these characteristics are an important consideration when delineating pesticide residue CSAs.

Promoting resistance by the emission of antibiotics from hospitals and households into effluent.

OBJECTIVE: There is growing concern about bacterial resistance to antimicrobials. The majority of antibiotics used are only partially metabolized after administration, and are released via patient excreta into the municipal sewage system. Data on the use of antibiotics and their emission into hospital effluent are not available. METHODS: Antibiotic consumption in Germany was calculated on the basis of five hospitals of varying size and medical service spectrum and on prescriptions issued by medical practitioners. The predicted environmental concentration (PEC) was calculated for hospital effluent and for municipal sewage. The PECs were compared both with published minimum inhibitory concentrations (MIC50) for sensitive pathogenic bacteria and with the predicted no-effect concentrations (PNECs). RESULTS: The amount of antibiotics emitted into hospital effluent may reach and exceed the MIC50 of susceptible pathogenic bacteria. The PEC/PNEC ratio is highest for hospital effluent (in some cases 10-20 times the MIC50) and frequently > 1 for municipal sewage. PECs are high enough for some compounds to have a PEC/PNEC ratio > 1 even in surface water. CONCLUSION: The volume of antibiotics used in hospitals and private households and released into effluent and municipal sewage indicates a selection pressure on bacteria. Steps should be taken to reduce the risk by proper handling of antibiotics and their residues both in hospitals and by private users.

Environmental auditing in hospitals: approach and implementation in an university hospital.

Medical audit in infection control today is accepted as an important element in the quality assurance of health care. In contrast, environmental auditing, which was approved in 1993 by the Council of the European Communities for industry ("Eco-Management and Audit Scheme-EMAS), has not so far been used as a tool to control and reduce environmental pollution caused by medical care in hospitals. The aim of this study was to investigate, whether environmental auditing in hospitals is useful. This process should also be cost effective. In this paper, methodological and organizational issues are described. Initially an environmental review of activities at the University Hospital, Freiburg and an eco-analysis of the input and output were performed. The first results of the study and a critical discussion will be presented in another paper.

Analysis of benzalkonium chloride in the effluent from European hospitals by solid-phase extraction and high-performance liquid chromatography with post-column ion-pairing and fluorescence detection.

A highly reproducible and specific method for the analysis of the quaternary ammonium compound, benzalkonium chloride, in effluents from European hospitals is presented. Benzalkonium chloride was extracted with end-capped RP-18 solid-phase cartridges and was selectively eluted. The resulting solution was analyzed by high-performance liquid chromatography (HPLC). After elution from the analytical column of the HPLC system, 9,10-dimethoxyanthracene-2-sulfonate was added continuously as a fluorescence marker, forming a hydrophobic ion-pair with benzalkonium chloride. The ion-pair was analyzed by fluorescence detection. The method was applied to highly complex effluent samples from different sized European hospitals. The measured concentrations were between 0.05 and 6.03 mg/l. The amounts emitted per bed and year were 4.5-362 g and did not correlate with the size of the hospital. The total amounts were 2.6-909 kg/year.

New and rapid fully automated method for determination of tazobactam and piperacillin in fatty tissue and serum by column-switching liquid chromatography.

A sensitive and rapid HPLC assay for determining tazobactam and piperacillin in fatty tissue and serum is described. While the common methods need liquid-liquid extraction before the injection in a automated column switching HPLC, the new method works by direct injection of the filtered tissue extract or diluted serum in a automated column switching HPLC without any other pre-treatment. This was performed by the use of a NH2-precolumn and enrichment/transfer at different pH-level. During the analyses, the NH2-precolumn was automatically regenerated with acetonitrile-water. The chromatogram peaks for piperacillin and tazobactam were identified by the retention time and quantified by peak area. The calibration curve was linear between 1 and 16 microg/ml. The quantification limit of tazobactam was about 1 microg/ml in fatty tissue extracts and in diluted serum (calculated for pure serum 2 microg/ml), respectively. For piperacillin it was less. The described procedure allows sample clean-up and determination of the antibiotic within 35 min. The chromatograms with this easy sample treatment had the same quantity of matrix peaks and in contrast to liquid-liquid extraction no loss of piperacillin. Because of the automatically rinsing of the NH2-precolumn during the chromatographic separation, more than 50 different biological samples could be measured with one NH2-precolumn without loss of performance.

[Roentgen contrast media, source for AOX-contamination of waste water by hospitals]. / Röntgenkontrastmittel, Quelle für die AOX-Belastung des Abwassers durch Krankenhäuser.

PURPOSE: To identify the sources for the exceeding of the upper limit of the AOX (adsorbable organic halogen, X = Cl, Br, I) in hospital waste-water and to estimate the contribution of hospital waste-water to the AOX of municipal waste-water. METHODS: For several hospitals with different medical directions, the expected AOX-concentration, as far as it is caused by iodine contrast media, was ascertained by the contrast media consumption and the water consumption. The results were compared with the measured AOX concentrations. RESULTS: The AOX-concentration of hospital waste-water varies between 0.41 mg/l and 0.94 mg/l. CONCLUSION: As a source of AOX iodine contrast media have been identified and may contribute considerably to the AOX. Hospitals with a radiological department may exceed the upper limit of the AOX which has to be observed in German municipal waste-water.

European hospitals as a source for platinum in the environment in comparison with other sources.

The concentration of platinum in the sewage of five European hospitals originating from excreted antineoplastic drugs, cisplatin and carboplatin, was analyzed in a short term study to provide an order of magnitude of Pt emissions from hospitals into aquatic environments. These emissions were compared with a rough estimation of emissions by cars. The average daily concentrations in the hospital effluents were approximately < 10-601 ng l-1 Pt (20-3580 ng l-1 in 2-h mixed samples). As expected from consumption data, the daily average concentrations should range from < 10-710 ng l-1 Pt. Platinum emitted by hospitals is 3.3-12.3% (1.3-14.3 kg per year) the estimated amount emitted by cars equipped with catalytic converters in the different European countries. Compared to platinum emissions from other sources, the effluents of hospitals are a minor source of platinum in municipal sewage, but they should not to be disregarded. Other possible sources for the emission of platinum into the environment should be considered in further investigations.

Drugs in the environment: emission of drugs, diagnostic aids and disinfectants into wastewater by hospitals in relation to other sources--a review.

After administration, pharmaceuticals are excreted by the patients into wastewater. Unused medications are sometimes disposed of in drains. The drugs enter the aquatic environment and eventually reach drinking water if they are not biodegraded or eliminated during sewage treatment. Additionally, antibiotics and disinfectants are supposed to disturb the wastewater treatment process and the microbial ecology in surface waters. Furthermore, resistant bacteria may be selected in the aeration tanks of STPs by the antibiotic substances present. Recently, pharmaceuticals have been detected in surface water, ground water and drinking water. However, only little is known about the significance of emissions from households and hospitals. A brief summary of input by different sources, occurrence, and elimination of different pharmaceutical groups such as antibiotics, anti-tumour drugs, anaesthetics and contrast media as well as AOX resulting from hospital effluent input into sewage water and surface water will be presented.

Mercury emissions from dental chairs by disinfection.

Dental aspirator kits are equipped with amalgam separators, which eliminate the particulate matter from the effluent. When the aspirator kits are disinfected, the disinfectant solution is in contact with the separated amalgams over night and over the weekend. Oxidizing components of the disinfectants dissolve mercury from the separated amalgam. The dissolved mercury is released into the environment along with the effluent on the beginning of the following workday. The degree of mercury remobilization depends on the amount and oxidizing power of the disinfectant components. The mercury concentrations measured in the effluent of the aspirator kits after the application of seven different disinfectants were 18.4 micrograms/l-1396 micrograms/l. The emission of mercury by dental aspirator kits is lowered substantially by using disinfectants which contain no oxidizing substances. Disinfecting of dental aspirator kits for hygienic reasons is not necessary. Therefore we propose only cleaning rather than disinfecting dental aspirator kits.

Biodegradability of some antibiotics, elimination of the genotoxicity and affection of wastewater bacteria in a simple test.

Most antibiotics and their metabolites are excreted by humans after administration and therefore reach the municipal sewage with the excretions. Only little is known about their biodegradability in aquatic environments. It was recognised that genotoxic substances may represent a health hazard to humans but also may affect organisms in the environment. Therefore, the biodegradability of some clinically important antibiotic drugs (ciprofloxacin, ofloxacin, metronidazole) and hereby the elimination of their genotoxicity was investigated as the first step of an environmental risk assessment using the Closed Bottle test (CBT) (OECD 301 D) and the SOS chromotest. Additionally, to assess toxicity of the antibiotics tested against aquatic bacteria (i) a growth inhibition test (GIT) with Pseudomonas putida was conducted, (ii) a toxicity control was used in the CBT and (iii) the colony forming units (CFUs) were monitored in the test vessels. Worst case concentrations of the antibiotics in hospital effluents were estimated and compared with minimum inhibitory concentrations for susceptible pathogenic bacteria and with the genotoxic potency in the SOS chromotest. Both the concentrations calculated for hospital effluents and the adverse effects in bacteria were in the same order of magnitude. None of the test compounds were biodegraded. The genotoxicity was not eliminated.

AOX-emissions from hospitals into municipal waste water.

Adsorbable organically bound halogens (AOX) are mostly persistent in the environment, and accumulate in the food web. Some of them are toxic to humans and other organisms. AOX were measured in the effluents from six German hospitals of different size and departments like internal medicine and ear-nose and throat (ENT) as well as from laundry, kitchen and laboratory. The concentrations in the day time mixed samples of the total effluent were 0.13 mg l(-1)-0.94 mg l-1 (phi = 0.43 mg l-1). For the separately investigated departments the lowest concentrations were found in the effluent from laundry and kitchen (0.015 mg l-1), and the highest ones in the effluents from the medical departments (0.12-1.71 mg l-1, phi 0.95 mg l-1 during the week and 0.06-0.10 mg l-1 at the week-end) and the laboratories (0.05-14.2 mg l-1, phi 2.73 mg l-1). The AOX concentration in night time mixed samples were 0.07-0.41 mg l-1 (phi = 0.41 mg l-1) for the total effluents and 0.25-2.64 mg l-1 (phi = 1.11 mg l-1) for medical departments. Concentrations expected by computing the input of AOX attributable to pharmaceuticals were between 11% and 16% for two hospitals and 7.7% for an ENT department. One additional important source of AOX in hospital effluents may be x-ray contrast media containing a iodine carbon bond.