Toomas Tenno

Polycyclic aromatic hydrocarbons (PAHs) in meat products and estimated PAH intake by children and the general population in Estonia

The concentrations of benzo[a]pyrene and 11 other polycyclic aromatic hydrocarbons (PAHs) were analysed from 322 commercial, cured meat products and 14 home-grilled meat samples as part of the Estonian food safety monitoring programme during 2001–2005. The maximum acceptable concentration of 5 µg kg−1 for benzo[a]pyrene was exceeded in 3.4% of samples. The highest PAH concentrations were detected in home-grilled pork samples. Using of disposable grilling unit resulted in 1.6 times higher PAH concentrations compared to the traditional wood-burning grill. The average intake of benzo[a]pyrene and sum of 12 PAHs from meat products was estimated for children (age 1–16 years) on the basis of an individual food consumption questionnaire and, for the general population, based on national food consumption data. The highest total PAH concentrations detected were 16 µg kg−1 in smoked meat and ham, 19 µg kg−1 in smoked sausage and 6.5 µg kg−1 in smoked chicken samples. Since smoking and grilling are prevalent meat-cooking methods in Estonia, the impact of meat products is assessed to be significant in overall PAH intake.

Nitrates and nitrites in vegetables and vegetable-based products and their intakes by the Estonian population

The content of nitrates were determined in 1349 samples of vegetables and ready-made food in 2003–2004 as a part of the Estonian food safety monitoring programme and the Estonian Science Foundation grant research activities. The results of manufacturers’ analyses carried out for internal monitoring were included in the study. The highest mean values of nitrates were detected in dill, spinach, lettuce and beetroot. The mean concentrations were 2936, 2508, 2167 and 1446 mg kg−1, respectively. The content of nitrites in samples was lower than 5 mg kg−1. In total, the mean intake of nitrates by the Estonian population was 58 mg day−1. The mean content of nitrates in vegetable-based infant foods of Estonian origin was 88 mg kg−1. The average daily intake of nitrates by children in the age group of 4–6 years was 30 mg. The infants’ average daily intake of nitrates from consumption of vegetable-based foods was 7.8 mg.

SUPEROXIDE ELECTRODE BASED ON COVALENTLY IMMOBILIZED CYTOCHROME C : MODELLING STUDIES

We have recently described an optimised electrode for the detection of enzymatic and cellular superoxide (O2*-) production based on cytochrome c immobilized covalently at a surface-modified gold electrode and applied this system to the study of free radical production by activated human glioblastoma cells. In this paper we report the development of a mathematical model for the O2*- electrode responding to enzymically produced O2*- which should enable the determination of absolute concentrations of O2*- in biological systems when this electrode is employed for direct, real-time monitoring of free radical release and interactions.

Electrochemical reduction of oxygen on thin-film Au electrodes in acid solution

The reduction of oxygen has been studied on thin-film gold electrodes using the rotating disk electrode (RDE) technique. Thin films of gold were prepared by vacuum evaporation onto glassy carbon and highly oriented pyrolytic graphite substrates. The surface morphology of the films was examined by atomic force microscopy. The kinetic parameters of O2 reduction have been determined and a Tafel slope of (−112±8)mVdec−1 was observed. The specific activity of the electrodes was almost independent of film thickness.

Step-wise temperature decreasing cultivates a biofilm with high nitrogen removal rates at 9°C in short-term anammox biofilm tests

ABSTRACT The anaerobic ammonium oxidation (anammox) and nitritation-anammox (deammonification) processes are widely used for N-rich wastewater treatment. When deammonification applications move towards low temperature applications (mainstream wastewater has low temperature), temperature effect has to be studied. In current research, in a deammonification moving bed biofilm reactor a maximum total nitrogen removal rate (TNRR) of 1.5 g N m−2 d−1 (0.6 kg N m−3 d−1) was achieved. Temperature was gradually lowered by 0.5°C per week, and a similar TNRR was sustained at 15°C during biofilm cultivation. Statistical analysis confirmed that a temperature decrease from 20°C down to 15° did not cause instabilities. Instead, TNRR rose and treatment efficiency remained stable at lower temperatures as well. Quantitative polymerase chain reaction analyses showed an increase in Candidatus Brocadia quantities from 5 × 103 to 1 × 107 anammox gene copies g−1 total suspended solids (TSS) despite temperature lowered to 15°C. Fluctuations in TNRR were rather related to changes in influent concentration. To study the short-term effect of temperature on the TNRR, a series of batch-scale experiments were performed which showed sufficient TNRRs even at 9–15°C (1.24–3.43 mg N g−1 TSS h−1, respectively) with anammox temperature constants (Q10) ranging 1.3–1.6. Experiments showed that a biofilm adapted to 15°C can perform N-removal most sufficiently at temperatures down to 9°C as compared with biofilm adapted to higher temperature. After biomass was adapted to 15°C, the decrease in TNRR in batch tests at 9°C was lower (15–20%) than that for biomass adapted to 17–18°C.

Estimation of biodegradation parameters of phenolic compounds on activated sludge by respirometry.

The bio-oxidation of phenol, catechol, resorcinol, m-cresol and 5-methylresorcinol on activated sludge was investigated by oxygen uptake measurements. In addition, the degradation of acetate with the same microbial population was studied. The substrate-dependent oxygen uptake data were analysed on the basis of the Michaelis-Menten kinetics. The extant kinetic parameters, the maximum rates of oxygen consumption and half-saturation constants for the processes with different substrates were determined. The simple respirometric approach also made it possible to determine the short-term oxygen demands of the substrates which formed 23-38% of the theoretical oxygen demand of the studied compounds.

Nitrites, nitrates and N-nitrosoamines in Estonian cured meat products: Intake by Estonian children and adolescents

The contents of nitrate, nitrite and N-nitrosoamines in commercial cured meat products on the Estonian market were determined for 2000–01 and 2003–04 as part of the Estonian food safety monitoring programme and the Estonian Science Foundation grant research activities. The maximum permitted levels of residual nitrites and nitrates were not exceeded in the samples analysed. However, a great variation in the content of nitrate, nitrite and N-nitrosoamines was found for all the products. The concentrations of these compounds in domestic cured meat products showed a decrease from year to year. The mean intake of nitrate, nitrite and N-nitrosoamines by Estonian children (n = 346) from cured meat products was calculated on the basis of individual intake data. The mean daily intake of nitrates was 1.7 mg, that of nitrites was 0.83 mg and that of N-nitrosoamines was 0.073 µg. In the 2000–01 study, the calculated nitrite intake exceeded the acceptable daily intake by up to 140% for 1–6-year-old children and up to 105% in 2003–04.

Dynamic model of amperometric biosensors. Characterisation of glucose biosensor output

An integrated model for the characterisation of the output signal course of oxidase-bound amperometric biosensors is presented and evaluated in the case of glucose biosensors. This model integrates two earlier proposed models, the model of oxygen transducer-based biosensors, allowing the prediction of steady state parameters from the transient response and the dynamic signal lag model, characterising the electrochemical diffusion-limited sensors. The integrated model allows the characterisation of the whole biosensor signal output, originating from the output curve itself with errors less than 3% and no need to determine the systems geometrical, diffusion and partition parameters.

Achieving nitritation and anammox enrichment in a single moving-bed biofilm reactor treating reject water

A biofilm with high nitrifying efficiency was converted into a nitritating and thereafter a nitritating–anammox biofilm in a moving-bed biofilm reactor at 26.5 (±0.5)°C by means of a combination of intermittent aeration, low dissolved oxygen concentration, low hydraulic retention time, free ammonia and furthermore, also by elevated HCO concentration. Nitrite-oxidizing bacteria (NOB) were more effectively suppressed by an enhanced HCO concentration range of 1200–2350 mg/L as opposed to free-ammonia-based process control where NOBs recovered from inhibition; the respective total-nitrogen removal rates were 0.3 kg N/(m3·d) and 0.2 kg N/(m3·d). The biofilm modification strategies resulted in a shift in bacterial community as the NOB Nitrobacter spp. were replaced with NOB belonging to the genus Nitrospiraspp. and were closely related to Candidatus Nitrospira defluvii. A community of anaerobic ammonium-oxidizing microorganisms –uncultured Planctomycetales bacterium clone P4 (closely related to Candidatus Brocadia fulgida) – was developed.

Calibration of glucose biosensors by using pre-steady state kinetic data.

A new method for biosensor calibration and data processing, allowing the prediction of steady state parameters from the analysis of transient response curves (Rinken et al., 1996. Analytical Letters 29, 859), has been evaluated in the case of an oxygen sensor based two-substrate enzyme electrode for glucose determination. The electrochemical glucose biosensor was prepared by covering the surface of oxygen sensor with glucose oxidase (EC 1.1.3.4) immobilized in nylon mesh. This decreased the oxygen flow to the sensor in the presence of glucose and resulted in time-dependent decrease of the biosensor signal. Except the lag period of the response in the beginning of the assay, the oxygen consumption by the immobilized enzyme was described by an exponential function: [formula: see text] The parameter C, which corresponded to the steady-state output of the biosensor, was found to be the most suitable for glucose determination. The non-linear fitting for data of over 1000 independent experiments to the equation above always revealed correlation coefficients greater than 0.97. The calculation of the steady state parameter from the transient phase data makes the analysis fast and precise, especially for sensors with thick membranes, being convenient to use in the case of enzyme electrodes. The theoretical essence of the parameter C also gives valuable information for the optimal design of biosensors.