Column Leaching using Dry Soil to Estimate Solid-Solution Partitioning Observed in Zero-Tension Lysimeters. 2. Trace Metals

The fundamental questions revolving around research into trace metals in soils are how much, and in what form, do metals exist in soil solutions. The mobile phase of soil solutions can be sampled by lysimeters, but cannot be consistently and accurately reproduced in laboratory extractions. We used a column leaching method developed specifically to produce solutions that were similar to those of lysimeters from northern forest podzolic soils. We hoped to yield reasonable estimates of the partitioning of Cd, Cu, Ni, Pb and Zn between the solid and solution phases observed in the field. The column leaching method produced solutions that were similar to lysimeter solutions in the concentrations of metals in solution. Partitioning coefficients (log K_d) calculated from average lysimeters solution concentrations ranged from 2.8 to 3.9 for Cd, 3.5 to 4.2 for Cu, 3.1 to 4.3 for Ni, 3.9 to 5.1 for Pb and 2.8 to 3.6 for Zn. Laboratory extractions produced very similar log K_d values ranging from 3.4 to 3.9 for Cd, 3.4 to 3.9 for Cu, 3.4 to 4.1 for Ni, 4.1 to 5.2 for Pb and 3.2 to 3.5 for Zn. According to a semi-mechanistic regression model based on observed lysimeter concentrations, the metal concentrations in solution were appropriate relative to known factors that influence metal partitioning in soils: pH and the concentrations of total metals and dissolved organic carbon. Partitioning coefficients based on laboratory extractions in the literature were on average an order of magnitude greater than those observed in lysimeters. When compared to the results of other laboratory extractions, the proposed extraction procedure appeared to be an effective method to estimate the chemistry of soil solutions in the field.     

PALAEOBIOLOGY OF THE CLIMACTICHNITES TRACEMAKER

Abstract:  Trace fossils such as Climactichnites offer rare insights into the palaeobiology of Cambrian soft-bodied animals, especially those that inhabited emergent sand flats and are not known from body fossils. Analysis of field and museum Climactichnites , together with experiments on the preservation of similar modern trails, indicates that the tracemaker was an elongate, bilaterally symmetrical, dorsoventrally flattened, soft-bodied animal with a muscular foot. These characteristics are consistent with the tracemaker being a primitive mollusc or mollusc-like animal. Unlike most Neoproterozoic and Cambrian molluscs, the tracemaker could reach considerable size; at up to c . 69 cm long, it was one of the largest Cambrian animals of its time. When moving on the sediment surface, locomotion resulted from muscular waves generated along the sole of its flexible foot; the foot was extended and then clamped onto the substrate. Contraction of pedal muscles then pulled the body forward. Sedimentary structures associated with Climactichnites  wilsoni , such as polygonal desiccation cracks, raindrop impressions, adhesion structures and gas escape structures demonstrate that the animal inhabited intermittently subaerially exposed environments. The tracemaker's method of locomotion is similar to that employed by modern intertidal gastropods, which make Climactichnites -like trails on exposed sand flats. However, these modern trails are not preserved because of erosion by wind, waves, tides and subsequent bioturbation. Abundant microbial sedimentary structures are associated with C. wilsoni , and together with low levels of vertical bioturbation, intimate that microbial binding may have mediated the preservation of these early mollusc trails.     

Methods for identifying precipitates and improving stability of chemically defined highly concentrated cell culture media

Currently, within the biopharmaceutical industry, media development is a key area of development as the ratios and concentrations of media components such as amino acids, metals, vitamins, sugars, salts, and buffering agents play arguably the largest role in cellular productivity and product quality. However, optimizing media for these targets often conflicts with solubility limitations and slow-rate chemical reactions that result in precipitation formation. Here we present methods such as inductively coupled plasma mass spectrometry (ICP-MS), X-ray fluorescence (XRF), colorimetry, and turbidity to identify multiple likely components of a complex precipitate that was observed in preparations of a custom nutrient feed medium across all storage conditions evaluated. Using these analytical methods, as well as adjustments to the formulation pH, increasing the pyruvate concentration, and removing sodium bicarbonate, we were able to extend the media shelf life from approximately 10 days to over 28 days. Alternatively, copper, selenium, and magnesium sources were removed from the media and no precipitation was observed until 32 days after prep, pointing to key metals as the probable root cause of precipitation. By analytically quantifying the precipitate using the methods above, instead of visual inspection, which is the current industry standard for media precipitation observation, we were better able to compare conditions to one another and relate them to the onset of precipitation. Cell culture performance and product quality remained comparable to the historical process despite the media formulation changes.     

Some Comments on the Selection of Human Intraspecies Uncertainty Factors

The Reference Dose (RfD) is used in the risk assessment of non-carcinogenic chemicals. It is derived by dividing a point of departure by the product of the uncertainty (UFs) and modifying factors (MFs). Separate UFs are used for different variables, e.g., intraspecies variation and, in general, each UF is an order of magnitude (10-fold). On the other hand, the MF is usually based on some known variable such as differences in absorption of a chemical from food and water and its default value is one. The USEPA's Integrated Risk Information System (IRIS) has 14 chemicals that have RfDs based on human studies. We examined those IRIS files to determine the rationale for setting human intraspecies uncertainty factors (UF_H). The first consideration was that the chemical had an adequate peer-reviewed human database. Without such, it would not be possible to derive an RfD based on human data. Ten of the 14 chemicals had an UF_H of 1 or 3; four of these were essential trace elements (ETEs). The rationales for using less than a 10-fold UF_H for the ETEs included; 1) nutritional data, 2) large human exposure groups, 3) minimal effect levels and/or 4) several studies with similar effect levels. For the other compounds, reasons included; 1) large human exposure groups, 2) a critical effect that was not adverse (cosmetic), 3) the most sensitive population was exposed, 4) the compound was on the FDA's “generally regarded as safe” (GRAS) list, 5) database uncertainties and 6) less-than-lifetime exposure adjusted for 70 years exposure. It is important to understand the reasons for selecting a UF_H of 1, or 3 as they will apply to future chemicals considered by the USEPA and other agencies.     

Enzymatic Pathways for the Consumption of Carbonyl Sulphide (COS) by Higher Plants*

Carbonyl sulphide (COS) is an important trace gas of the atmosphere. Considerable uncertainties remain concerning the global sinks of COS. Vegetation is believed to be an unqualified sink in the global cycle of COS. We investigated whether there is an enzymological background for the consumption of COS by higher plants in analogy to CO₂. Photometric measurements demonstrated that all enzymes involved in C0₂ assimilation by higher plants can also metabolise COS. The key enzyme for COS metabolism in higher plants is carbonic anhydrase, an enzyme which probably directly splits COS into C0₂ and H₂S. Such a pathway would explain the observed deposition of COS to vegetation.     

Coral skeletons: storage and recovery of environmental information

Understanding the nature and causes of past global change is a key to understanding what may happen in the future. The discovery, nearly 25 years ago, of annual density bands in skeletons of long-lived, massive corals promised high-resolution proxy climate records for tropical oceans. The tropics are regions of major importance to the global climate system and they are poorly represented by high-resolution proxy climate records such as tree rings, ice cores and historical documents. In this review we examine the principles and procedures underlying routine recovery and interpretation of information from proxy environmental recorders. We summarize an extensive literature which indicates that coral skeletons are excellent archives for considerable and diverse environmental information. We show that this potential has not been fully realized, largely because corals seemed to yield inconsistent, sometimes conflicting, information. We discuss ways in which much of this confusion is resolved by new understanding of coral skeletal growth mechanisms. We also examine several records which indicate that corals can meet requirements for reconstruction of useful, reliable environmental information.     

Radiochemical neutron activation analysis in the life sciences

The contribution of radiochemical neutron activation analysis (RCNAA) to a better understanding of trace element analytics and physiology in the life sciences is outlined. Now, various non-nuclear powerful techniques for trace element analysis have become available, competing with RCNAA. This necessitates re-evaluation of the position of RCNAA, in particular versus inductively coupled plasmamass spectrometry (ICP-MS). On basis of the characteristic features of RCNAA and the capabilities of various competing non-nuclear analytical techniques, future niches for RCNAA in the analytical market are indicated. Presentation in memory of the late prof. Dr Jacques Versieck.     

Role of some trace metal ions in placental membrane lipid peroxidation

The antioxidative and/or pro-oxidative potential of three trace metal ions, namely aluminum (Al), manganese (Mn), and selenium (Se), has been studied. The effect of Al and Mn was found to be anion independent. The pro-oxidative potential of Al was more prominent than its antioxidative potential. This may be due to its redox inert nature. The increase in lipid peroxidation rates in placental syncytiotroblast membranes may contribute to the etiology of aluminum toxicity. Selenium had an antioxidative potential only in the whole-cell homogenate. This appears to be mediated by glutathione peroxidase of which Se is a cofactor. Manganese proved to be the trace metal ion of choice. It decreased the production of thiobarbituric acid reactive substances (TBARS). This may be due to its capacity to quench the superoxide anion and hydroxyl radicals and also due to its chain-breaking capacity. During the present course, ferrous-ascorbate mediated lipid peroxidation has been studied using various combinations of FeSO₄ and ascorbic acid. Extrapolating the combined ratio of the individual combination as substrate concentration ([S]) and treating the observed amount of malondialdehyde (MDA) produced equivalent to initial velocity (v _i ), as in the case of enzymatic studies, the data were treated according to Michaelis-Menten kinetics and the values of k _c and C _max have been calculated.     

Consequences of trace metal variability and supplementation on Chinese hamster ovary (CHO) cell culture performance: A review of key mechanisms and considerations

Trace metals are supplied to chemically-defined media (CDM) for optimal Chinese hamster ovary (CHO) cell culture performance during the production of monoclonal antibodies and other therapeutic proteins. However, lot-to-lot and vendor-to-vendor variability in raw materials consequently leads to an imbalance of trace metals that are supplied to CDM. This imbalance can yield detrimental effects rooted in several primary mechanisms and pathways including oxidative stress, apoptosis, lactate accumulation, and unfavorable glycan synthesis. Recent research endeavors involve supplying zinc, copper, and manganese to CDM in excess to further maximize culture productivity and product quality. These treatments significantly impact critical quality attributes and furthermore highlight the degree to which trace metal availability can affect CHO cell culture performance. This review highlights the role of trace metal variability, supplementation, and interplay on key cellular mechanisms responsible for overall culture performance and the production and quality of therapeutic proteins.