Titanium dioxide (Ti0 2 ) has been noted (US Federal Register, 43FR38206, 25 August 1978) to be a safe physical sunscreen because it reflects and scatters UVB and UVA in sunlight. However, Ti0 2 absorbs about 70% of incident UV, and in aqueous environments this leads to the generation of hydroxyl radicals which can initiate oxidations. Using chemical methods, we show that all sunscreen Ti0 2 samples tested catalyse the photo-oxidation of a representative organic substrate (phenol). We also show that sunlight-illuminated Ti0 2 catalyses DNA damage both in vitro and in human cells. These results may be relevant to the overall effects of sunscreens.

Radiation-induced acute myeloid leukemias (AMLs) in the mouse are characterized by chromosome 2 deletions. Previous studies showed that a minimal deleted region (mdr) of approximately 6.5 cM is lost from one homologue in chromosome 2-deleted AMLs. An AML tumor suppressor gene is proposed to map within this mdr. In this study, we refine the mdr to a I cM interval between markers D2Mit126 and D2Mit185 by microsatellite analysis of 21 primary radiation-induced F I AMLs. The construction of a partial yeast artificial chromosome (YAC) contig spanning the mdr and the location of six known genes indicated that the 1 cM mdr is homologous to human 11p11-12, a region implicated in some human AMLs. Screening of five cell lines derived from primary radiation-induced AMLs for homozygous loss of microsatellites and genes mapping within the mdr revealed loss of both copies of the hemopoietic tissue-specific transcription factor Sfpi1(PU.1/Spi1) in one cell line. Studies of primary and F1 AMLs failed to implicate Sfpi1 as the AML tumor suppressor gene. YAC contig construction, together with data suggesting that the critical gene flanks Sfpi1, represents significant progress toward identifying an AML tumor suppressor gene.

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The synthetic oestrogens, stilboestrol, hexoestrol, and dienoestrol give color reactions with nitric and nitrous acids, bromine, and certain phenol reagents, some of which can be adapted to their colorimetric determination. The use of Folin and Ciocalteu's phenol reagent is described for determination of the hormones in pharmaceutical products, using a Lumetron photoelectric colorimeter. The interference of other oestrogens and of phenolic preservatives and bactericides is considered and reference is made to a means of identifying the hormones by color reactions with antimony pentachloride in ethylene dichloride, and with an acetic – phosphoric acid reagent.