The oxidation states of arsenic in well-water from a chronic arsenicism area of northern Mexico

Aquifers in the Región Lagunera in northern Mexico are heavily contaminated with arsenic. The range of total arsenic concentrations in 128 water samples analyzed was 0.008 to 0.624 mg litre(-1), and concentrations greater than 0.05 mg litre(-1) were found in 50% of them. Approximately 400 000 people living in rural areas were exposed to high As concentrations. Most of the As was in inorganic form and pentavalent arsenic [As(V)] was the predominant species in 93% of the samples. In 36% of the samples, however, variable percentages (20-50) of trivalent As [As(III)] were found. Organic arsenicals were present in very small amounts. Since As(III) is several times more toxic than As(V), we suggest that periodic studies be performed on the As(III)/As(V) ratio in wells whose total As concentrations are above 0.05 mg litre(-1), in combination with epidemiological studies to evaluate possible differences in health effects produced by different As species.     

Gametogenic periodicity in the chemosynthetic cold-seep mussel “<Emphasis Type="Italic">Bathymodiolus” childressi</Emphasis>

The gametogenic periodicity of the cold seep mussel “Bathymodiolus” childressi was analysed from a time series of samples from depths of ∼ 650 m surrounding the Brine Pool cold seep on the continental slope of the northern Gulf of Mexico. Occasional samples were retrieved from Bush Hill and GC 234 for comparison. At the Brine Pool, both females and males showed strong reproductive periodicity with the initiation of gametogenesis from December to March, followed by a period of gamete growth or proliferation and spawning from October to February. Gametogenesis was synchronized at all three sites. Gametogenic periodicity appears to be correlated with surface production that peaks during the winter months. Downward flux of detritus during this period may provide food for the planktotrophic larvae and also supplementary nutrition for the adult, which has chemosynthetic bacterial symbionts but is also capable of filter feeding. Individuals in all three populations carried parasites and these were especially common at Bush Hill and GC234, where it is suggested they have a major impact on reproductive output.