Mobilisation, alteration, and redistribution of monosulfidic sediments in inland river systems

The accumulation of monosulfidic sediments in inland waterways is emerging as a major environmental issue. Mobilisation and suspension of monosulfidic sediments can result in deoxygenation, acidification of the water column and mobilisation of trace metals. The controls on monosulfidic sediment mobilisation and the critical thresholds for its scour and entrainment have not been established. This study examines the effect of a minor flood event (average return interval of 5 years) on sulfidic sediment scour in the Wakool River in southern NSW, Australia. Five profiles were sampled within a small (~300 m) reach before and after a minor flood event to determine the degree of sediment scour and transport. The results indicate substantial scour of both monosulfidic sediments and underlying bed sediments (approximately 2100 m(3)). Changes in the sediment geochemistry suggest large concentrations of monosulfidic sediments had been suspended in the water column, partially-oxidised and redeposited. This is supported by (210)Pb results from one of the profiles. These results suggest that these monosulfidic sediments can move as bed load during minor flood events.

Monosulfidic black ooze accumulations in sediments of the Geographe Bay area, Western Australia

Mobilisation of sedimentary monosulfidic black ooze (MBO) may result in rapid deoxygenation and acidification of surface waters, and release of potentially toxic metals. This study examines the extent and nature of MBO accumulation in the Geographe Bay area, Western Australia. MBO accumulations were found to be widespread in benthic sediments of the Geographe Bay area with acid-volatile sulfide (AVS) contents as high as 320 μmol g(-1). The MBO materials often had unusually high dissolved sulfide (S(-II)) concentrations in their pore-waters (up to 610 mg L(-1)) and elevated elemental sulfur (S(0)) contents (up to 51 μmol g(-1)). Dissolved S(-II) is able to accumulate due to limited iron availability and S(0) is largely its partial oxidation product. The availability of organic carbon and Fe limited MBO accumulation at many sites. A comparison of AVS and simultaneously extracted metal (SEM) concentrations has shown that metals are likely to be bound in sulfide complexes.

Iron-monosulfide oxidation in natural sediments: resolving microbially mediated S transformations using XANES, electron microscopy, and selective extractions

Iron-monosulfide oxidation and associated S transformations in a natural sediment were examined by combining selective extractions, electron microscopy and S K-edge X-ray absorption near-edge structure (XANES) spectroscopy, The sediment examined in this study was collected from a waterway receiving acid-sulfate soil drainage. It contained a high acid-volatile sulfide content (1031 micromol g(-1)), reflecting an abundance of iron-monosulfide. The iron-monosulfide speciation in the initial sediment sample was dominated by nanocrystalline mackinawite (tetragonal FeS). At near-neutral pH and an 02 partial pressure of approximately 0.2 atm, the mackinawite was found to oxidize rapidly, with a half-time of 29 +/- 2 min. This oxidation rate did not differ significantly (P < 0.05) between abiotic versus biotic conditions, demonstrating that oxidation of nanocrystalline mackinawite was not microbially mediated. The extraction results suggested that elemental S (S8(0)) was a key intermediate S oxidation product Transmission electron microscopy showed the S8(0) to be amorphous nanoglobules, 100-200 nm in diameter. The quantitative importance of S8(0) was confirmed by linear combination XANES spectroscopy, after accounting for the inherent effect of the nanoscale S8(0) particle-size on the corresponding XANES spectrum. Both the selective extraction and XANES data showed that oxidation of S8(0) to SO4(2-) was mediated by microbial activity. In addition to directly revealing important S transformations, the XANES results support the accuracy of the selective extraction scheme employed here.

Women with phenylketonuria: successful management of pregnancy and implications

Dietary management of five pregnancies in two women (sisters) with classical phenylketonuria (PKU) is described. One child died neonatally of congenital heart disease and one pregnancy miscarried. Of the three surviving children the only physically and mentally normal child, followed up to eight years, was born after a carefully planned pregnancy with strict dietary control preconceptually and throughout pregnancy. One pregnancy treated dietetically from six weeks gestation resulted in a child mentally normal at seven years but born with oesophageal atresia. The third surviving child is microcephalic and mentally retarded but dietetic treatment did not commence till 28 weeks gestation. It is concluded that to be effective, dietary control must be instituted preconceptually.

The needs of the intellectually handicapped

There are about 10 000 intellectually handicapped people in New Zealand. Most are fit, healthy, mobile adults with individual needs and the same rights as other citizens. Most can be trained to live semi-independent lives, living within the community in family-type homes, flats or small hostels, provided properly organised and efficient community based support services are developed. A minority present major problems in behaviour, or lack mobility, or are multi-handicapped and require permanent institutional care. Such institutions should be small and located in the community that they serve. There is a need for action, not words, in developing the provisions for the intellectually handicapped in our community.

Progeny, pregnancy and phenylketonuria

Two sisters were diagnosed as having phenylketonuria at the age of 13 years and eight years and having Wechsler IQs of 48-58 and 71-81 respectively. Neither girl was treated with diet. At the age of 21 years the older girl became pregnant. Her blood phenylalanine level was 23mg/100 ml. A low phenylalanine diet, instituted from the 10th week of gestation, maintained her blood phenylalanine levels below 6mg/100ml for the rest of the pregnancy. A female baby, of birth weight 3216g and normal skull size, was delivered at term. The baby died at 14 days of congenital heart disease. Pregnancy in a phenylketonuric woman carries high risks to the fetus. A generation of treated phenylketonuric girls is approaching reproductive life, and doctors and the girls themselves need to be alerted to these risks and the need for strict dietary control during pregnancy. There are probably unrecognised women in the community with phenylketonuria or with hyperphenylalaninaemia whose babies face similar risks. Identification of these women could be achieved by antenatal Guthrie testing.