It seems tea (Camellia sinensis, not herbal teas) may be potentially hazardous depending on quantity taken and how much already ingested from other sources.  My take is that you would probably have to consume very large amounts per day, though and I am guessing that  one or two cups a day would be within safe levels.  --  Marilyn

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http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=14963548&itool=iconfft&query_hl=3&itool=pubmed_docsum
Fluoride and aluminum in teas and tea-based beverages.
Departamento de Ciencias Fisiol gicas, Faculdade de Odontologia de Piracicaba, Universidade Estadual de Campinas, Piracicaba, SP, Brazil.

OBJECTIVE: To evaluate fluoride and aluminum concentration in herbal, black, ready-to-drink, and imported teas available in Brazil considering the risks fluoride and aluminum pose to oral and general health, respectively. METHODS: One-hundred and seventy-seven samples of herbal and black tea, 11 types of imported tea and 21 samples of ready-to-drink tea were divided into four groups: I-herbal tea; II-Brazilian black tea (Camellia sinensis); III-imported tea (Camellia sinensis); IV-ready-to-drink tea-based beverages. Fluoride and aluminum were analyzed using ion-selective electrode and atomic absorption, respectively. RESULTS: Fluoride and aluminum levels in herbal teas were very low, but high amounts were found in black and ready-to-drink teas. Aluminum found in all samples analyzed can be considered safe to general health. However, considering 0.07 mg F/kg/day as the upper limit of fluoride intake with regard to undesirable dental fluorosis, some teas exceed the daily intake limit for children. CONCLUSIONS: Brazilian and imported teas made from Camellia sinensis as well as some tea-based beverages are sources of significant amounts of fluoride, and their intake may increase the risk of developing dental fluorosis.

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Fluoride concentration and pH of iced tea products.
Department of Pediatric Dentistry, Medical Center of Odontology, Justus Liebig University of Giessen, Germany.

The objective of this study was to determine the fluoride concentration and pH of 44 iced tea samples and hence to assess the possible role of these beverages as systemic fluoride source as well as their potential cariogenic and erosive character. Ten tea samples were available as a granular instant powder, and 34 as ready-to-drink liquid products. The iced teas contained different types of sugar alone or in combination with maltodextrin, glucose syrup and noncaloric sweeteners. In one product, only acesulfame and aspartame were established. All samples contained lemon juice or citric acid as an additive. The pH ranged from 4.04 to 2.63 and the titrated amount of base to pH 7.0 from 0.75 to 2.39 mmol NaOH/50 ml. The fluoride concentrations measured were <0.6 ppm in 14 products, 0.6-1.0 ppm in 10 products, 1.1-1.5 ppm in 16 products, 1.6-2.0 ppm in 2, and >2.0 ppm in another 2 products. In conclusion, most of the iced teas studied contained considerable fluoride concentrations. If infants ingest larger amounts of them because of their sweet taste, there is a risk of uncontrolled overdosing as a result of additional fluoride intake from other sources at the same time. Furthermore, the majority of the products revealed a highly cariogenic character and finally, all the iced teas appear to be acidic enough to cause dental erosion if these refreshments were excessively consumed from nursing bottles. Copyright 2002 S. Karger AG, Basel

PMID: 12459612 [PubMed - indexed for MEDLINE]

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Fluorides in groundwater, soil and infused black tea and the occurrence of dental fluorosis among school children of the Gaza strip.
Institute of Environmental Geochemistry, University of Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany. [log in to unmask]

The purpose of this study was to determine the fluoride levels in water, soil and tea, and to identify the major fluoride minerals in soil that supply water with fluoride ions. Another aim was to study the prevalence of dental fluorosis in permanent dentition of the school children of the Gaza Strip. Monitoring of fluoride levels in 73 groundwater wells and 20 topsoil samples for the last three years revealed a general trend of increasing from north to south of the Gaza Strip. A linear regression analysis found a correlation coefficient of r=0.93 between the fluoride concentrations in groundwater and soil for the same geographic areas. However, the X-ray diffraction technique (XRD) results showed that none of the four major fluoride minerals were detected in the tested soil samples; the PHREEQC model showed that fluorite (CaF2) was the main donating mineral of fluoride ions to groundwater. A high positive correlation was found between fluoride concentrations in groundwater and occurrence of dental fluorosis. Among 353 school children of the five geographic areas of the Gaza Strip the prevalence of dental fluorosis was 60%, and 40% had no signs of fluorosis in their permanent dentitions. The highest occurrence, 94%, was in Khan Yunis, followed by 82% in Rafah, 68% in the middle area, 29% in Gaza and the lowest occurrence of 9% was in the northern area. These percentages were directly proportional to the average content of fluoride in groundwater of each area: 2.6, 0.9, 1.7, 1.2, and 0.7 ppm, respectively. The exception was Rafah where people drank from new groundwater wells that have been dug in the last 10 years. The occurrence of the disease was due to intake of high amounts of fluorides in drinking water, tea and fish. Communication with population indicated a heavy intake of tea starting from a very young age; not uncommonly tea is put in nursing bottles. No significant correlation was found between prevalence figures and gender or age groups. This high prevalence indicates a need to examine other sources of F including diet.

PMID: 15384727 [PubMed - indexed for MEDLINE]