ABSTRACT
Nine urban intertidal regions in Burrard Inlet, Vancouver, British Columbia, Canada, were sampled for plastic debris. Debris included macro and micro plastics and originated from a wide diversity of uses ranging from personal hygiene to solar cells. Debris was characterized for its polymer through standard physiochemical characteristics, then subject to a weak acid extraction to remove the metals, zinc, copper, cadmium and lead from the polymer. Recently manufactured low density polyethylene (LDPE), nylon, polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS) and polyvinyl chloride (PVC) were subject to the same extraction. Data was statistically analyzed by appropriate parametric and non-parametric tests when needed with significance set at P < 0.05. Polymers identified in field samples in order of abundance were; PVC (39), LDPE (28), PS (18), polyethylene (PE, 9), PP (8), nylon (8), high density polyethylene (HDPE, 7), polycarbonate (PC, 6), PET (6), polyurethane (PUR, 3) and polyoxymethylene (POM, 2). PVC and LDPE accounted for 46% of all samples. Field samples of PVC, HDPE and LDPE had significantly greater amounts of acid extracted copper and HDPE, LDPE and PUR significantly greater amounts of acid extracted zinc. PVC and LDPE had significantly greater amounts of acid extracted cadmium and PVC tended to have greater levels of acid extracted lead, significantly so for HDPE. Five of the collected items demonstrated extreme levels of acid extracted metal; greatest concentrations were 188, 6667, 698,000 and 930 µgg-1 of copper, zinc, lead and cadmium respectively recovered from an unidentified object comprised of PVC. Comparison of recently manufactured versus field samples indicated that recently manufactured samples had significantly greater amounts of acid extracted cadmium and zinc and field samples significantly greater amounts of acid extracted copper and lead which was primarily attributed to metal extracted from field samples of PVC. Plastic debris will affect metals within coastal ecosystems by; 1) providing a sorption site (copper and lead), notably for PVC 2) desorption from the plastic i.e., the "inherent" load (cadmium and zinc) and 3) serving as a point source of acute trace metal exposure to coastal ecosystems. All three mechanisms will put coastal ecosystems at risk to the toxic effects of these metals.
Subject(s)
Ecosystem , Metals/chemistry , Plastics/chemistry , Trace Elements/chemistry , AdsorptionABSTRACT
We describe the key features of a pre-production, slot-scan digital mammography system. A number of these units have been used in clinical studies over the past year for the purpose of demonstrating their equivalence to the conventional film-screen devices. Since the clinical data has not yet been fully analyzed, it is not possible to make definitive claims. However, with hundreds of patients examined, the results appear to leave very little doubt the SenoScan digital mammography system will prove equivalent to the conventional technology. The detector developed for this system has a sensitive area 1.0 cm wide by 22 cm long. It is constructed by abutting four charge-coupled-device (CCD) chips, which are optically coupled to thallium-doped cesium iodide scintillator by means of a thin fiber optic plate. Scanning is accomplished by attaching the detector to a rigid arm that swings in an arc, with the axis of rotation collinear with the X-ray tube focal spot. The total scan time for the 30 cm image width is less than 6 s, with an effective exposure time of either 0.2 or 0.4 s. Two resolution modes are available: 0.054 mm or 0.027 mm square pixel size; in the latter mode both the image length and width are halved, as is the scan velocity, so that the scan time remains the same. To compensate for the low X-ray utilization efficiency of the slot geometry, a tungsten rhenium target X-ray tube is employed. It is rated at 8 kW on the 0.3 mm focal spot; when used with a heat exchanger, it has been found to provide the patient throughput needed in a busy clinical practice.
