Fluoride Ingestion After Brushing with a Gel Containing a High Concentration of Fluoride

The aim of the study was to evaluate the amount of fluoride remaining in the oral cavity of children after brushing with fluoride gel (1.25% F). The study involved six groups of 7-year-old and six groups of 11-year-old children. The procedure was carried out according to the manufacturer’s recommendations. Fluoride concentrations were determined using ion-selective fluoride electrode. No statistically significant difference was found between the amount of fluorides that remained in the oral cavity of younger and older age group (1.2 and 1.3 mg, respectively; p > 0.05). The amount of fluorides swallowed during the procedure in both age groups proves to be within acceptable limit, as far as risk of acute poisoning symptoms is concerned. The individual daily fluoride exposure during the day of procedure seems to be twice as high compared to average fluoride intake from diet and dentifrice, and it does not exceed Tolerable Upper Intake Level for children more than 8. In younger children, it seems justifiable to reduce the amount of the preparation applied on a toothbrush, especially when daily use of the gel is recommended.     

Urinary Fluoride Reference Values Determined by a Fluoride Ion Selective Electrode

As fluoride has a very short half-life in the body and the major route for fluoride excretion is via the kidney, human exposure is best measured in urine, where the concentration is expected to be highest. The urinary fluoride concentrations of 167 healthy Japanese adults were determined by means of a fluoride ion selective electrode. When the results were corrected for a specific gravity ρ = 1.024 g cm⁻³, the histogram of urinary fluoride concentrations highly skewed toward low values with sharp peakedness (skewness = 1.56, kurtosis = 3.08). The normality of the log-transformed histogram (skewness = 0.12, kurtosis = 0.07) and the straight line on log-probability paper clearly showed a key feature of lognormal distribution of urinary fluoride. A geometric mean (GM) of 613.8 μg/l and 95% confidential interval (CI) of 241.0–1633.1 μg/l were established as reference values for urinary fluoride. The results presented in this study will be useful as guidelines for the biological monitoring of fluoride in normal subjects and individuals at risk of occupational or environmental fluoride exposure.     

Gastrointestinal Absorption and Renal Excretion of Fluoride After Ingestion of a High-Fluoride Dentifrice

This study aimed to evaluate the gastrointestinal absorption and renal excretion of fluoride after the ingestion of high-fluoride dentifrice. Twelve volunteers participated in this in vivo, crossover, and blinded study. In three experimental phases, the volunteers were randomly assigned to one of three treatment groups, who ingested either the following: distilled and deionized water (control), conventional dentifrice (1100 μg/g), or high-fluoride dentifrice (5000 μg/g). Both dentifrices contained fluoride in the form of NaF/SiO₂. To determine the rate of fluoride absorption, non-stimulated saliva was collected for up to 120 min after ingestion and the area under the curve of the salivary fluoride concentration was plotted as a function of time and the maximum concentration determined. All urine produced during the 24 h before and after ingestion was collected, and urinary excretion was calculated from the difference between the urinary fluoride concentrations in the two periods. A specific ion electrode coupled to an ion analyzer was used to measure fluoride concentrations. Statistical analysis was performed by ANOVA followed by Tukey’s test with p set at 5%. All measured parameters were highest after the ingestion of the dentifrice with 5000 μg/g (p < 0.001), confirming that this has an increased level of bioavailable fluoride compared with the conventional dentifrice. The high-fluoride dentifrice increases the concentration of salivary fluoride, which may explain its greater anticaries effect. However, it poses a potential risk of causing dental fluorosis and so should not be used by children.

     

Influence of Methionine and Vitamin E on Fluoride Concentration in Bones and Teeth of Rats Exposed to Sodium Fluoride in Drinking Water

Increased exposure to fluorine-containing compounds leads to accumulation of fluorides in hard tissues of bones and teeth, which may result in numerous skeletal and dental disorders. This study evaluates the influence of methionine and vitamin E on fluoride concentration in bones and teeth of rats subjected to long-term exposure to sodium fluoride in drinking water. The study was conducted in 30 3-month-old female Wistar FL rats. The animals were divided into five groups, six rats per group. The control group consisted of rats receiving only distilled water as drinking water. All other groups received NaF in the amount of 10 mg/kg of body mass/day in their drinking water. In addition, respective animal groups received: NaF + Met group—10 mg of methionine/kg of body mass/day, NaF + Met + E group—10 mg of methionine/kg of body mass/day and 3 mg of vitamin E (tocopheroli acetas)/rat/day and NaF + E group—3 mg of vitamin E/rat/day. Femoral bones and incisor teeth were collected for the study, and the fluoride concentration was determined using a fluoride ion-selective electrode. Fluoride concentration in both bones and teeth was found to be higher in the NaF and NaF + Met groups compared to the control group. In groups NaF + Met + E and NaF + E, the study material contained much lower fluoride concentration compared to the NaF group, while the effect was more prominent in the NaF + E group. The results of the studies indicate that methionine and vitamin E have opposite effects on accumulation of fluorides in hard tissue in rats. By stimulating fluoride accumulation, methionine reduces the adverse effect of fluorides on soft tissue, while vitamin E, which prevents excessive accumulation of fluorides in bones and teeth, protects these tissues from fluorosis. Therefore, it seems that combined application of both compounds would be optimal for the prevention of the adverse effects of chronic fluoride intoxication.     

Fluoride and environmental health: a review

The relationship between environmental fluoride and human health has been studied for over 100 years by researchers from a wide variety of disciplines. Most scientists believe that small amounts of fluoride in the diet can help prevent dental caries and strengthen bones, but there are a number of adverse affects that chronic ingestion at high doses can have on human health, including dental fluorosis, skeletal fluorosis, increased rates of bone fractures, decreased birth rates, increased rates of urolithiasis (kidney stones), impaired thyroid function, and lower intelligence in children. Chronic occupational exposure to fluoride dust and gas is associated with higher rates of bladder cancer and variety of respiratory ailments. Acute fluoride toxicity and even death from the ingestion of sodium fluoride pesticides and dental products have also been reported. The distribution of fluoride in the natural environment is very uneven, largely a result of the geochemical behavior of this element. Fluorine is preferentially enriched in highly evolved magmas and hydrothermal solutions, which explains why high concentrations are often found in syenites, granitoid plutonic rocks, alkaline volcanic, and hydrothermal deposits. Fluoride can also occur in sedimentary formations that contain fluoride-bearing minerals derived from the parent rock, fluoride-rich clays, or fluorapatite. Dissolved fluoride levels are usually controlled by the solubility of fluorite (CaF₂); thus, high concentrations are often associated with soft, alkaline, and calcium-deficient waters. Although much is known about the occurrence and health effects of fluoride, problems persist in Third World countries, where populations have little choice in the source of their drinking water and food. However, even in developed nations, fluoride ingestion can exceed the recommended dose when sources other than drinking water are ignored.     

Chronic Fluoride Exposure Has a Role in Etiology of Coronary Artery Ectasia: Sialic Acid/Glycosaminoglycan Ratio

The sialic acid/glycosaminoglycan ratio was determined in 35 coronary artery ectasia patients and 35 control subjects to determine the possible role of fluoride in the etiology of the disease. The coronary artery ectasia patients and controls were selected from subjects who underwent coronary angiography. The mean serum sialic acid level was significantly lower in patients with coronary artery ectasia (CAE) than in controls (340.3 ± 28.6 vs. 427.0 ± 15.9 μg/mL, respectively; p < 0.001). The mean serum glycosaminoglycan level was significantly higher in patients with CAE than in controls (5,013.1 ± 158.6 vs. 3,833.6 ± 237.1 μg/mL, respectively; p < 0.001). The sialic acid/glycosaminoglycan ratio in patients with coronary artery ectasia was significantly lower than in controls (0.068 ± 0.007 vs. 0.111 ± 0.005; p < 0.001). There was more than 38.7% reduction in this ratio in patients with CAE when compared with controls. We demonstrated that chronic fluoride exposure has an important role in pathogenesis of coronary artery ectasia.     

The use of silica gel prepared by sol-gel method and polyurethane foam as microbial carriers in the continuous degradation of phenol

A mixed microbial culture was immobilized by entrapment into silica gel (SG) and entrapment/ adsorption on polyurethane foam (PU) and ceramic foam. The phenol degradation performance of the SG biocatalyst was studied in a packed-bed reactor (PBR), packed-bed reactor with ceramic foam (PBRC) and fluidized-bed reactor (FBR). In continuous experiments the maximum degradation rate of phenol (q _s ^max) decreased in the order: PBRC (598 mg l⁻¹h⁻¹) > PBR (PU, 471 mg l⁻¹h⁻¹) > PBR (SG, 394 mg l⁻¹h⁻¹) > FBR (PU, 161 mg l⁻¹h⁻¹) > FBR (SG, 91 mg l⁻¹ h⁻¹). The long-term use of the SG biocatalyst in continuous phenol degradation resulted in the formation of a 100–200 μm thick layer with a high cell density on the surface of the gel particles. The abrasion of the surface layer in the FBR contributed to the poor degradation performance of this reactor configuration. Coating the ceramic foam with a layer of cells immobilized in colloidal SiO₂ enhanced the phenol degradation efficiency during the first 3 days of the PBRC operation, in comparison with untreated ceramic packing. Received: 2 December 1999 / Revision received: 2 February 2000 / Accepted: 4 February 2000     

不同剂量的多乐氟对学龄前儿童尿氟浓度的影响

目的:观察儿童使用不同剂量的多乐氟氟化钠护齿剂(Duraphat)对其尿氟浓度的影响,为Duraphat应用于群防群治提供理论依据。方法:采用氟离子选择电极法,将53名3~4岁儿童按班别分成三组,分别使用0.2 m L及0.05 m L Duraphat涂布儿童牙齿,检测涂氟前和涂氟后1、2、3 d的尿氟浓度,并进行组内和组间比较。结果:各组使用Duraphat后尿氟浓度逐渐增加,涂氟后2 h开始与涂氟前比较差异均有统计学意义(P0.05),涂氟后3~4 h尿氟浓度达到高峰,至21 h后与涂氟前比较差异无统计学意义(P0.05);3岁0.2 m L组与0.05 m L组在涂氟后2~4 h的尿氟浓度比较差异有显著性(P0.05),其他时间比较均无显著性差异(P0.05);0.05 m L3岁组与4岁组比较尿氟浓度无明显差别(P0.05);3岁初次用氟组和4岁多次用氟组涂氟前尿氟无显著差异(P0.05)。结论:儿童口腔局部用氟对其尿氟浓度有影响,随局部用氟剂量的增加而增加;年龄对儿童尿氟浓度无明显影响;Duraphat在体内无远期氟蓄积,在一定剂量内使用Duraphat可起到较好的防龋效果。     

Effects of Fluoride on Synaptic Membrane Fluidity and PSD-95 Expression Level in Rat Hippocampus

The objective of this study is to investigate the neurotoxicity of drinking water fluorosis on rat hippocampus. Just weaning male Sprague–Dawley rats were randomly divided into four groups and given 15, 30, and 60 mg/L NaF solution and distilled water, respectively, for 9 months. The fluidity of brain synaptic membrane and expression level of postsynaptic density 95 (PSD-95) were tested. Results showed that the fluidity of brain synaptic membrane decreased gradually with increasing of fluoride concentration, and it was significantly decreased (P < 0.05) in moderate-fluoride group compared with control group, and expression level of PSD-95 was significantly decreased (P < 0.01) in moderate-fluoride group when compared with that of control group. These results indicate that decrease of synaptic membrane fluidity and PSD-95 expression level may be the molecular basis of central nervous system damage caused by fluoride intoxication; PSD-95 in CA3 region of hippocampus is probably a target molecule for fluoride.     

Alterations in Electrocardiographic Parameters after Subacute Exposure of Fluoride and Ameliorative Action of Aluminium Sulphate in Goats

Fluorosis or crippling disease is one of the existing environmental challenges for animal and human beings in most parts of the globe. In the present study, sodium fluoride alone and with aluminium sulphate (ameliorative agent) was administered orally daily for 30 days in healthy goats of group 1 and 2, respectively, to access the effect on the electrocardiogram. All waves of Lead I, Lead II, Lead III, aVR, aVL and aVF in electrocardiographs were recorded before and after 30 days exposure of fluoride. A significant (P < 0.05) increase in P–R, Q–T and S–T intervals were observed in goats of group 1 as compared to their pre treatment values. The T wave duration was also significantly (P < 0.05) prolonged and as a result, bradycardia was observed after subacute exposure of fluoride for 30 days in group 1. But, in group 2, no such changes were observed. On the basis of results, it may be concluded that subacute toxicity of fluoride produces significant changes in different waves of electrocardiogram and aluminium sulphate has ameliorative efficacy.     

Salivary Hsp72 does not track exercise stress and caffeine-stimulated plasma Hsp72 responses in humans

Heat shock protein 72 (Hsp72) has been detected within saliva, and its presence may contribute to oral defence. It is currently unknown how physiological stress affects salivary Hsp72 or if salivary Hsp72 concentrations reflect plasma Hsp72 concentrations. We studied the effect of exercise upon salivary Hsp72 expression, and using caffeine administration, investigated the role of sympathetic stimulation upon salivary Hsp72 expression. Six healthy males performed two treadmill running exercise bouts in hot conditions (30°C) separated by 1 week in a randomized cross-over design, one with caffeine supplementation (CAF) the other with placebo (PLA). Plasma and saliva samples were collected prior to, during and post-exercise and assayed for Hsp72 concentration by ELISA. Exercise significantly increased plasma Hsp72, but not salivary Hsp72 concentration. Mean salivary Hsp72 concentration (5.1 ± 0.8 ng/ml) was significantly greater than plasma Hsp72 concentration (1.8 ± 0.1 ng/ml), and concentrations of salivary and plasma Hsp72 were unrelated. Caffeine supplementation and exercise increased the concentration of catecholamines, salivary α-amylase and total protein, whilst the salivary Hsp72:α-amylase ratio was lower in CAF. Salivary Hsp72 was not altered by exercise stress nor caffeine supplementation, and concentrations did not track plasma Hsp72 concentration.     

Pentachlorophenol biodegradation kinetics of an oligotrophic fluidized-bed enrichment culture

A fluidized-bed reactor (FBR) was used to enrich an aerobic chlorophenol-degrading microbial culture. Long-term continuous-flow operation with low effluent concentrations selected oligotrophic microorganisms producing good-quality effluent for pentachlorophenol(PCP)-contaminated water. PCP biodegradation kinetics was studied using this FBR enrichment culture. The results from FBR batch experiments were modeled using a modified Haldane equation, which resulted in the following kinetic constants: q _max = 0.41 mg PCP mg protein⁻¹ day⁻¹, K _S = 16 μg l⁻¹, K _i = 5.3 mg l⁻¹, and n = 3.5. These results show that the culture has a high affinity for PCP but is also inhibited by relatively low PCP concentrations (above 1.1 mg PCP l⁻¹). This enrichment culture was maintained over 1 year of continuous-flow operation with PCP as the sole source of carbon and energy. During continuous-flow operation, effluent concentrations below 2 μg l⁻¹ were achieved at 268 min hydraulic retention time (t _HR) and 2.5 mg PCP l⁻¹ feed concentration. An increase in loading rate by decreasing t _HR did not significantly deteriorate the effluent quality until a t _HR decrease from 30 min to 21 min resulted in process failure. Recovery from process failure was slow. Decreasing the feed PCP concentration and increasing t _HR resulted in an improved process recovery. Received: 10 October 1996 / Received revision: 21 January 1997 / Accepted: 24 January 1997     

Buffering effect of a prophylactic gel on dental plaque in institutionalised elderly

Objectives: The effect of multiple daily applications of a prophylactic gel, with buffering substances, on plaque acidogenicity in elderly institutionalised individuals was evaluated. Background: Many elderly suffer from reduced salivary flow, poor oral hygiene and increased levels of cariogenic bacteria and are considered to be at an increased risk for coronal and root caries. Reinforcing the buffering capacity of dental plaque by the addition of substances such as bicarbonate and phosphates may decrease their caries activity. Materials and methods: Fourteen elderly, with subjective dry mouth, were treated for 16‐day‐periods at random with: (i) Profylin fluoride gel with buffering components; (ii) Profylin fluoride gel without buffering components and (iii) rinsing with water. Applications were made four times a day and each period was followed by a 2‐week wash‐out period. The plaque pH was registered after a carbohydrate challenge and the following were recorded before and after each test period: stimulated salivary secretion rate, buffer capacity, number Colony Farming Units (CFU) mutans streptococci, lactobacilli and a sample of Candida albicans on oral mucosa. Results: Eleven participants (mean age 76.6 years) fulfilled the study. Changes in plaque pH measurements, when calculated as area under the curve (AUC_6.2 and AUC_5.7) values (pH × min), before and after each of the three treatments, showed no significant differences. A tendency to a higher plaque acidogenicity and amount of cariogenic microorganisms was found after the gel treatments. C. albicans was found in low levels. Conclusion: Frequent applications of the gel did not result in an improved neutralising effect in the elderly. This may be caused by a combination of several factors, such as the level of oral dryness of the individuals and low solubility, release and retention of the gel substances in plaque. Instead, an increased plaque acidogenicity was noted.     

Treatment of cyanide-containing wastewater from the food industry in a laboratory-scale fixed-bed methanogenic reactor

During the process of producing cassava starch from Manihot esculenta roots, large amounts of cyanoglycosides were released, which rapidly decayed to CN⁻ following enzymatic hydrolysis. Depending on the varying cyanoglycoside content of the cassava varieties, the cyanide concentration in the wastewater was as high as 200 mg/l. To simulate anaerobic stabilization, a wastewater with a chemical oxygen demand (COD) of about 20 g/l was prepared from cassava roots and was fermented in a fixed-bed methanogenic reactor. The start-up phase for a 99% degradation of low concentrations of cyanide (10 mg/l) required about 6 months. After establishment of the biofilm, a cyanide concentration of up to 150 mg CN⁻/l in the fresh wastewater was degraded during anaerobic treatment at a hydraulic retention time of 3 days. All nitrogen from the degraded cyanide was converted to organic nitrogen by the biomass of the effluent. The cyanide-degrading biocoenosis of the anaerobic reactor could tolerate shock concentrations of cyanide up to 240 mg CN⁻/l for a short time. Up to 5 mmol/l NH₄Cl (i.e. 70 mg N/l = 265 mg NH₄Cl/l) in the fresh wastewater did not affect cyanide degradation. The bleaching agent sulphite, however, had a negative effect on COD and cyanide removal. For anaerobic treatment, the maximum COD space loading was 12 g l⁻¹ day⁻¹, equivalent to a hydraulic retention time of 1.8 days. The COD removal efficiency was around 90%. The maximum permanent cyanide space loading was 50 mg CN⁻ l⁻¹ day⁻¹, with tolerable shock loadings up to 75 mg CN⁻ l⁻¹day⁻¹. Under steady-state conditions, the cyanide concentration of the effluent was lower than 0.5 mg/l. Received: 15 August 1997 / Received revision: 10 October 1997 / Accepted: 14 October 1997     

Effect of Fluoride Exposure on Serum Glycoprotein Pattern and Sialic Acid Level in Rabbits

This study describes the effects of fluoride exposure on the protein profile, glycoprotein pattern, and total sialic acid concentration of serum in rabbits. For this aim; 20 healthy New Zealand rabbits were used. The rabbits were divided into two equal groups each with ten animals according to their weighing: control group and experimental group. The rabbits in control group were given drinking tap water containing 0.29 mg/l sodium fluoride and experimental group received the same tap water to which was added 40 mg/l sodium fluoride for 70 days. Blood samples were taken from each rabbit on day 70. Serum fluoride concentrations were measured by a fluoride-specific ion electrode in serum. The fluoride levels in the serum were found as 18.4 (±1.58) μg/L in control and 301.3 (±52.18) μg/L in fluoride exposed rabbits. The sialic acid levels were found as 69.2 (±0.32) mg/dL in control and 43.4 (±0.13) mg/dL in fluoride exposed group. The electrophoretic patterns of serum proteins, glycoproteins, and total sialic acid concentration were determined. Fifteen different protein fractions with molecular weights ranging from 22 to 249 kDa were displayed in the serum protein electrophoretic gel of both groups. The raw concentrations of the protein fractions decreased in fluoride exposed rabbits as compared with the control rabbits. The serum glycoprotein pattern revealed seven major protein bands from 47 to 167 kDa in experimental and control groups. The slight decrease of raw concentration of the protein bands in glycoprotein pattern of serum was observed in fluoride toxication comparing to control. The results suggest that serum TSA determination and serum protein electrophoresis can be used to evaluate prognosis of fluoride exposure as a supplementary laboratory test in combination with clinical and other laboratory findings of fluorosis.     

Elevation of PTH and PTHrp Induced by Excessive Fluoride in Rats on a Calcium-deficient Diet

Study on the role of parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrp) in the process of skeletal fluorosis, involved especially in calcium deficiency, is rare. We evaluated the level of serum PTH and mRNA expression of PTHrp in femur when rats were exposed to excessive fluoride with low-calcium diet. Wistar rats (n = 60) was divided into four groups, a control group, fluoride group, low-calcium group, and low-calcium fluoride group. The fluoride groups were treated with fluoride by drinking tap water containing 100 mg F-/L. The low-calcium diet contained 0.05% calcium. Serum was collected in the first, fourth, eighth, and 12th of phase for the detemination of PTH and Ca²⁺. RNA extraction from femora was used to analyze the mRNA express of PTHrp, osteopontin (OPN), and osteocalcin (OCN) after 12 weeks of fluoride dosing. Results showed that serum PTH increased gradually with the extension of fluoride exposure, but Ca²⁺ decreased, both of which embodied a time-dependent relationship. Cotreatment of excessive fluoride with low-calcium diet largely stimulated the secretion of PTH. The low dietary calcium markedly increased mRNA expression of PTHrp in animals with fluoride treatment. Expression of OPN and OCN significantly increased in the rats treated with excessive fluoride and low-calcium diet. We demonstrated that fluoride by itself affected the body's calcium metabolism and stimulate the secretion of PTH. PTH may play an important role in anabolic effect of excessive fluoride on bone turnover of skeletal fluorosis and calcium deficiency exacerbated the action of PTH and PTHrp on the characteristic bone lesion of fluorosis.     

Ingestion of crude oil: effects on digesta retention times and nutrient uptake in captive river otters

Studies following the Exxon Valdez oil spill in Prince William Sound, Alaska indicated that river otters (Lontra canadensis) from oiled regions displayed symptoms of degraded health, including reduced body weight. We examined the fate of ingested oil in the digestive tract and its effects on gut function in captive river otters. Fifteen wild-caught males were assigned to three groups, two of which were given weathered crude oil in food (i.e., control, 5 ppm day⁻¹, and 50 ppm day⁻¹) under controlled conditions at the Alaska Sealife Center. Using glass beads as non-specific digesta markers and stable isotope analysis, we determined the effects of ingested oil on retention time and nutrient uptake. Our data indicated that oil ingestion reduced marker retention time when we controlled for activity and meal size. Fecal isotope ratios suggested that absorption of lipids in the oiled otters might have been affected by reduced retention time of food. In addition, a dilution model indicated that as much as 80% of ingested oil was not absorbed in high-dose animals. Thus, while the ingestion of large quantities of weathered crude oil appears to reduce absorption of oil hydrocarbons and may alleviate systemic effects, it may concurrently affect body condition by impacting digestive function. Accepted: 18 May 2000     

Effects of pH profiles on nisin fermentation coupling with foam separation

Online foam separation was proposed to recover nisin during fermentation of Lactococcus lactis subsp. lactis ATCC 11454. Firstly, the optimal pH profile of nisin fermentation was investigated including different realkalization set values and pH drop gradients. Then the selected pH profiles of 5.75 ± 0.05 and 6.25–5.75 (±0.02) were used to perform nisin fermentation coupling with foam separation. The results showed that pH profile of 5.75 ± 0.05 was better than that of 6.25–5.75 (±0.02) for online foam separation. With the optimal pH profile, an aeration of 20 ml min⁻¹ that started at 8 h of incubation and lasted for 2 h resulted in 6.6 times higher specific productivity than that of the fermentation without aeration. Nisin synthesis was therefore prolonged with low sucrose concentration in the culture broth, which indicated that the feedback inhibition of nisin is more influential than the substrate limitation of sucrose in the late phase of nisin fermentation. Total nisin production (4,870 ± 180 IU ml⁻¹) was increased by 30.3% with online foam separation. This effective online recovery method for nisin production could be easily scaled up due to the facile operation of foaming process.     

Repeated application of carvone-induced bacteria to enhance biodegradation of polychlorinated biphenyls in soil

Carvone, the principal component of spearmint oil, induces biodegradation of polychlorinated biphenyls (PCB) by Arthrobacter sp. strain B1B. This study investigated the effectiveness of the repeated application of carvone-induced bacteria for bioremediation of Aroclor-1242-contaminated soil. Control treatments compared a single inoculation of carvone-induced cells, repeated applications of noninduced cells, and repeated applications of cell-free carvone/fructose medium. The results showed that repeated application of carvone-induced bacteria was the most effective treatment for mineralizing PCB, resulting in 27 ± 6% degradation of Aroclor 1242 after 9 weeks; whereas a single application of cells resulted in no significant degradation. Addition of cell-free, carvone/fructose medium resulted in 10% degradation of PCB, which suggests that this treatment stimulated biodegradation of PCB by the indigenous microflora. The di- and trichlorobiphenyls were the most readily degraded congeners. More highly chlorinated congeners, which had been previously shown to be degraded in liquid culture, were not substantially degraded in soil, indicating that low bioavailability may have limited their degradation. With the development of new technology, which permits automated in situ fermentation and delivery of degrader microorganisms, the repeated application of carvone-induced bacteria may facilitate bioremediation of PCB-contaminated soils. Received: 7 January 1998 / Received revision: 18 June 1998 / Accepted: 27 June 1998     

Production of 1,3-propanediol by Clostridium butyricum in continuous culture with cell recycling

The continuous fermentation of 1,3-propanediol from glycerol by Clostridium butyricum was subjected to cell recycling by filtration using hollow-fibre modules made from polysulphone. The performance of the culture system was checked at a retention ratio (dilution rate/bleed rate) of 5, dilution rates between 0.2 h⁻¹ and 1.0 h⁻¹ and glycerol input concentrations of 32 g l⁻¹ and 56 g l⁻¹. The near-to-optimum propanediol concentration of 26.5 g l⁻¹ (for 56 g l⁻¹ glycerol) was maintained up to a dilution rate of 0.5 h⁻¹ and then decreased while the propanediol productivity was highest at 0.7 h⁻¹. The productivity could be increased by a factor of four in comparison to the continuous culture without cell recycling. By application of the model of Zeng and Deckwer [(1995) Biotechnol Prog 11: 71–79] for cultures under substrate excess, it was shown that the limitations resulted exclusively from product inhibition and detrimental influences from the cell recycling system, such as shear stress, were not involved. Received: 20 October 1997 / Received revision: 12 December 1997 / Accepted: 14 December 1997