Genotoxic effects of fluoride: a controversial issue

Fluoride is an element which is widely distributed in our environment. Its cariostatic efficacy has been well documented, and numerous studies indicate that at a concentration of 1 ppm in water, fluoride is beneficial for caries prevention and does not appear to exacerbate any diseases. Currently, more than half the American population is consuming naturally or artificially fluoridated water and efforts are being made to increase this proportion significantly. In addition, the multiple use of fluoride for dental caries prevention is clearly increasing. It is a common practice to use fluoride in a variety of delivery systems, including dentifrices, mouthrinses, pediatric supplements, and professional or self-applied topical solutions or gels as well as dental restorative materials. These dental products may contain fluoride in concentrations as high as 12,300 ppm. Increasing exposure of the population to fluoride has raised questions about the safety of this measure and has established the need for objective reappraisal. In particular, interest has developed regarding the genotoxic effects of fluoride. Unfortunately, there is, at present, only a limited amount of information available concerning the potential genotoxic effects of fluoride, and the results that have been published are contradictory and often very confusing. A review of the literature clearly indicates the importance of, and necessity for, clarifying the conflicts and controversies regarding this important issue.

Genotoxic effects of fluoride evaluated by sister-chromatid exchange

The purpose of this investigation was to study the genotoxic potential of fluoride (in the form of sodium fluoride, NaF) using in vitro and in vivo sister-chromatid exchange (SCE) assays with Chinese hamster cells. The NaF concentrations used in cultures of Chinese hamster ovary (CHO) cells ranged from 0 to 6.3 mM, both with and without S9 activation. Fluoride analysis of the culture medium demonstrated that it contained little indigenous fluoride, and the concentration of added fluoride was not affected by the components of the medium or the S9 mix. The CHO cells cultured in 6.3 mM NaF almost vanished, and at the concentration of 5.3 mM NaF in cultures without S9 microsome, only M1 cells were observed. In in vivo studies, Chinese hamsters were intubated with NaF dosages of 0, 0.1, 1.0, 10, 60 and 130 mg/kg, and the bone marrow (CHBM) cells were examined for SCE frequencies. Bone fluoride data showed that the intubated NaF was effectively absorbed. Death occurred in 3 of the 8 animals given 130 mg NaF/kg. The results indicated that NaF, in dosages up to 5.3 mM in CHO cell cultures and 130 mg/kg in in vivo CHBM cells, did not significantly increase the SCE frequencies over those observed in the negative (distilled water) controls. However, examination of the cell cycle revealed an inhibitory effect of NaF on cell proliferation with doses of NaF at or greater than 1.0 mM in cultured CHO cells and at or greater than 60 mg NaF/kg in in vivo CHMB cells. The results of the present study indicated an inhibition of the cell cycle and death of the cells with increasing concentrations of fluoride but not effect of fluoride on SCE frequency in CHO and CHBM cells.

Cancer of esophagus and esophagogastric junction: analysis of results of 1,025 resections after 5 to 20 years

Resection was carried out in 1,025 of 1,654 patients with cancer of the esophagus or esophagogastric junction at the Peking Medical College Hospitals in China from 1953 through 1973. All cancers of the esophagus were squamous cell carcinomas except for five adenocarcinomas. A lesion localized within the esophageal wall was found in 55% and lymph node metastasis in 41.3% of the patients undergoing resection. All cancers of the esophagogastric junction were adenocarcinomas. The tumor had invaded beyond the boundaries of the stomach in 76.7% of these patients, and positive nodes were found in 61% of the patients. The rate of resectability was 81.2% for esophageal cancer and 74% for cancer of the esophagogastric junction. Surgical mortality after resection was 4.9% (50/1,025). The 5-year survival after resection was 20.9% (214/1,025). Better results were found following complete resection: 24% (210/875) for all patients, 28.2% (162/575) for patients with cancer of the esophagus, and 16% (48/300) for patients with cancer of the esophagogastric junction. Late survival at 10, 15, and 20 years after resection of esophageal cancer was 20%, 12%, and 7.4%, respectively. The favorable prognostic factors after resection of esophageal cancer were tumor of the lower third of the esophagus, the absence of lymph node involvement, and the presence of a localized lesion. The 5-year survival for patients with cancer of the lower third of the esophagus was 32.7%. It was 64.2% for patients with a localized lesion with negative nodes in this subgroup.

Observations on Baiji (Lipotes vexillifer) and finless porpoise (Neophocaena asiaeorientalis) in the lower reaches of the Chang Jiang

Lipotes usually occurs in pairs or in small loose groups. The calves are born in March-April. The Finless porpoises are usually seen in groups of five or six individuals. The blow of Lipotes lasts 0.2-0.6 sec and that of Neophocaena 0.2-0.5 sec. In Lipotes, a short dive would take 10-20 sec and a long dive up to 1-2 min (average value being 31 sec). In Neophocaena a long dive would reach a maximum of 65 sec with an average of 17.5 sec. Lipotes has a pair of functional eyes. The selective secondary atrophy of a number of eye muscles and nerves and the position of the eyes in the head correspond with the physical conditions of the environments, so that the field of vision is directed forwards and upwards. When pursued by motor boat, both species react with a long dive and a change of direction under water. With the Baiji this would occasionally cause fatal injuries by the propeller of the ship. Such a case seems much less often with Neophocaena. The population of Lipotes is at present very small. In the stretch of the river (between Nanjing and Taiyangzhou) under exploration, we found scarcely more than one dolphin per 4 km. The cause for its scarcity is mostly due to accidents or wounds caused by propellers.