41 research outputs found
An Assessment of the Model of Concentration Addition for Predicting the Estrogenic Activity of Chemical Mixtures in Wastewater Treatment Works Effluents
The effects of simple mixtures of chemicals, with similar mechanisms of action, can be predicted using the concentration addition model (CA). The ability of this model to predict the estrogenic effects of more complex mixtures such as effluent discharges, however, has yet to be established. Effluents from 43 U.K. wastewater treatment works were analyzed for the presence of the principal estrogenic chemical contaminants, estradiol, estrone, ethinylestradiol, and nonylphenol. The measured concentrations were used to predict the estrogenic activity of each effluent, employing the model of CA, based on the relative potencies of the individual chemicals in an in vitro recombinant yeast estrogen screen (rYES) and a short-term (14-day) in vivo rainbow trout vitellogenin induction assay. Based on the measured concentrations of the four chemicals in the effluents and their relative potencies in each assay, the calculated in vitro and in vivo responses compared well and ranged between 3.5 and 87 ng/L of estradiol equivalents (E2 EQ) for the different effluents. In the rYES, however, the measured E2 EQ concentrations in the effluents ranged between 0.65 and 43 ng E2 EQ/L, and they varied against those predicted by the CA model. Deviations in the estimation of the estrogenic potency of the effluents by the CA model, compared with the measured responses in the rYES, are likely to have resulted from inaccuracies associated with the measurement of the chemicals in the extracts derived from the complex effluents. Such deviations could also result as a consequence of interactions between chemicals present in the extracts that disrupted the activation of the estrogen response elements in the rYES. E2 EQ concentrations derived from the vitellogenic response in fathead minnows exposed to a series of effluent dilutions were highly comparable with the E2 EQ concentrations derived from assessments of the estrogenic potency of these dilutions in the rYES. Together these data support the use of bioassays for determining the estrogenic potency of WwTW effluents, and they highlight the associated problems for modeling approaches that are reliant on measured concentrations of estrogenic chemicals
Coastal Upwelling Supplies Oxygen-Depleted Water to the Columbia River Estuary
Low dissolved oxygen (DO) is a common feature of many estuarine and shallow-water
environments, and is often attributed to anthropogenic nutrient enrichment from
terrestrial-fluvial pathways. However, recent events in the U.S. Pacific
Northwest have highlighted that wind-forced upwelling can cause naturally
occurring low DO water to move onto the continental shelf, leading to
mortalities of benthic fish and invertebrates. Coastal estuaries in the Pacific
Northwest are strongly linked to ocean forcings, and here we report observations
on the spatial and temporal patterns of oxygen concentration in the Columbia
River estuary. Hydrographic measurements were made from transect (spatial
survey) or anchor station (temporal survey) deployments over a variety of wind
stresses and tidal states during the upwelling seasons of 2006 through 2008.
During this period, biologically stressful levels of dissolved oxygen were
observed to enter the Columbia River estuary from oceanic sources, with minimum
values close to the hypoxic threshold of 2.0 mg Lâ1. Riverine
water was consistently normoxic. Upwelling wind stress controlled the timing and
magnitude of low DO events, while tidal-modulated estuarine circulation patterns
influenced the spatial extent and duration of exposure to low DO water. Strong
upwelling during neap tides produced the largest impact on the estuary. The
observed oxygen concentrations likely had deleterious behavioral and
physiological consequences for migrating juvenile salmon and benthic crabs.
Based on a wind-forced supply mechanism, low DO events are probably common to
the Columbia River and other regional estuaries and if conditions on the shelf
deteriorate further, as observations and models predict, Pacific Northwest
estuarine habitats could experience a decrease in environmental quality
Architecture of the Oman-UAE ophiolite : evidence for a multi-phase magmatic history
The OmanâUnited Arab Emirates ophiolite is the
worldâs largest ophiolite. It is divided into 12 separate faultbounded
blocks, of which the northern three lie wholly or
partly in the United Arab Emirates. Extensive mapping has
shown that the United Arab Emirates blocks contain mantle
and crustal sections which correspond to the classic
âPenrose conferenceâ ophiolite definition but which are
cut by a voluminous later magmatic sequence including
ultramafic, mafic and felsic components. Samples from the
later magmatic sequence are dated at 96.4±0.3, 95.74±0.3
and 95.2±0.3 Ma; the early crustal section, which has not
been dated directly, is thus constrained to be older than c.
96.4 Ma. Petrological evidence shows that the early crustal
section formed at a spreading ridge, but the later magmatic
sequence was formed from hydrous magmas that produced
different mineral crystallisation sequences to normal midocean
ridge basalt (MORB). Mineral and whole-rock
geochemical analyses show that the early crustal rocks are
chemically similar to MORB, but the later magmatic
sequence has chemical features typically found in suprasubduction
zone (SSZ) settings. The ophiolite in the United
Arab Emirates thus preserves clear evidence for two stages
of magmatism, an early episode formed at a spreading
centre and a later episode associated with the onset of
subduction. Similar two-stage magmatism has been recognised
in the Oman sector, but the United Arab Emirates
contains the most voluminous SSZ magmatism yet described
from this ophiolite