Risikobetrachtung: Probleme, Definitionen, Methoden im Zuge der Altstoff-Bewertung

Vgl. auch UWSF 2/91, S. 102 ff.     

Long-term records of cadmium and silver contamination in sediments and oysters from the Gironde fluvial-estuarine continuum - evidence of changing silver sources

The Gironde fluvial estuarine system is impacted by historic metal pollution (e.g. Cd, Zn, Hg) and oysters (Crassostrea gigas) from the estuary mouth have shown extremely high Cd concentrations for decades. Based on recent work (Chiffoleau et al., 2005) revealing anomalously high Ag concentrations (up to 65 mg kg⁻¹; dry weight) in Gironde oysters, we compared long-term (∼1955-2001) records of Ag and Cd concentrations in reservoir sediment with the respective concentrations in oysters collected between 1979 and 2010 to identify the origin and historical trend of the recently discovered Ag anomaly. Sediment cores from two reservoirs upstream and downstream from the main metal pollution source provided information on (i) geochemical background (upstream; Ag: ∼0.3 mg kg⁻¹; Cd: ∼0.8 mg kg⁻¹) and (ii) historical trends in Ag and Cd pollution. The results showed parallel concentration-depth profiles of Ag and Cd supporting a common source and transport. Decreasing concentrations since 1986 (Cd: from 300 to 11 mg kg⁻¹; Ag: from 6.7 to 0.43 mg kg⁻¹) reflected the termination of Zn ore treatment in the Decazeville basin followed by remediation actions. Accordingly, Cd concentrations in oysters decreased after 1988 (from 109 to 26 mg kg⁻¹, dry weight (dw)), while Ag bioaccumulation increased from 38 up to 116 mg kg⁻¹, dw after 1993. Based on the Cd/Ag ratio (Cd/Ag ∼ 2) in oysters sampled before the termination of zinc ore treatment (1981-1985) and assuming that nearly all Cd in oysters originated from the metal point source, we estimated the respective contribution of Ag from this source to Ag concentrations in oysters. The evolution over the past 30 years clearly suggested that the recent, unexplained Ag concentrations in oysters are due to increasing contributions (>70% after 1999) by other sources, such as photography, electronics and emerging Ag applications/materials.     

Cyanide phytoremediation by water hyacinths (Eichhornia crassipes)

Although cyanide is highly toxic, it is economically attractive for extracting gold from ore bodies containing only a few grams per 1000 kg. Most of the cyanide used in industrial mining is handled without observable devastating consequences, but in informal, small-scale mining, the use is poorly regulated and the waste treatment is insufficient. Cyanide in the effluents from the latter mines could possibly be removed by the water hyacinth Eichhornia crassipes because of its high biomass production, wide distribution, and tolerance to cyanide (CN) and metals. We determined the sodium cyanide phytotoxicity and removal capacity of E. crassipes. Toxicity to 5-50 mg CN L(-1) was quantified by measuring the mean relative transpiration over 96 h. At 5 mgCNL(-1), only a slight reduction in transpiration but no morphological changes were observed. The EC(50) value was calculated by probit analysis to be 13 mgCNL(-1). Spectrophotometric analysis indicated that cyanide at 5.8 and 10 mgL(-1) was completely eliminated after 23-32 h. Metabolism of K(14)CN was measured in batch systems with leaf and root cuttings. Leaf cuttings removed about 40% of the radioactivity from solution after 28 h and 10% was converted to (14)CO(2); root cuttings converted 25% into (14)CO(2) after 48 h but only absorbed 12% in their tissues. The calculated K(m) of the leaf cuttings was 12 mgCNL(-1), and the V(max) was 35 mg CN(kg fresh weight)(-1)h(-1). Our results indicate that E. crassipes could be useful in treating cyanide effluents from small-scale gold mines.     

放牧阉牦牛提前出栏甲烷排放强度减排潜力探讨

以阉牦牛提前出栏项目活动为例,按照2006年IPCC国家温室气体清单优良做法指南的计量方法,在同等牧草利用量的前提下,分别对4岁和7岁阉牦牛一生CH4排放总量和单位体重CH4排放量(即排放强度)进行了初步比较分析.发现在同等牧草利用量的基础上,由于饲养一头7岁阉牦牛一生所消耗的牧草量相当于可饲养2.1头4岁的阉牦牛所消耗的牧草量,所以从CH4排放总量而言,前者一生排放CH4总量比后者少86.3 kg.然而,由于后者总体重比前者重192 kg,所以,后者的单位体重CH4排放强度(以CH4/体重计)只有0.973 kg·kg-1,而前者为1.374 kg·kg-1.根据排放强度的概念,在同等牧草消耗量的基础上,如果将一头7岁阉牦牛替代成饲养2.1头4岁的阉牦牛,可以多生产192 kg的活体重,在同样生产192 kg活重的基础上,利用替代法估算后者饲养方式比前者饲养方式可以实现77 kg CH4减排量,即相当于总减排1.6 t CO2当量.因此,基于排放强度减排而不是总量减排的概念,提前出栏有较大的CH4减排潜力.     

Environmental assessment of green hardboard production coupled with a laccase activated system

European consumption of wood-based panels reached record levels in recent years driven mostly by demand from end-use sectors: residential construction, furniture, cabinets, flooring and mouldings. The main panel types are composite boards such as particleboard, high density fiberboard (HDF), medium-density fiberboard (MDF) and other adhesively bonded composites such as plywood and wet-process fiberboard (hardboard). The synthetic resins used in their manufacture come from non-renewable resources, such as oil and gas. Several consequences are associated to this type of adhesives: variation in the availability and cost of these wood adhesives depends on raw materials, the formaldehyde emissions as well as the limited recyclability of the final product. Hence, in the search for alternatives to petroleum-based wood adhesives, efforts are being devoted to develop adhesives by using phenolic substitutes based on lignin, tannin or starch. In this context, the forest industry is increasingly approaching to enzyme technology in the search of solutions. The main goal of this study was to assess the environmental impacts during the life cycle of a new process for the manufacture of hardboards manufacture, considering the use of a two-component bio-adhesive formulated with a wood-based phenolic material and a phenol-oxidizing enzyme. This new product was compared to the one manufactured with the conventional phenol-formaldehyde resin. The study covers the life cycle of green hardboards production from a cradle-to-gate perspective, analysing in detail the hardboard plant and dividing the process chain in three subsystems: Fibers Preparation, Board Forming and Board Finishing.Auxiliary activities such as chemicals, bio-adhesive, wood chips, thermal energy and electricity production and transport were included within the system boundaries.Global warming (GW), photochemical oxidant formation (PO), acidification (AC) and eutrophication (EP) were the impact categories analysed in this study. Additionally, the cumulative energy demand was evaluated as another impact category. According to the results, four stages significantly influenced the environmental burdens of the production system: laccase production, on-site thermal energy and electricity production as well as wood chipping stage. Due to the environmental impact associated to the production of green bonding agents, a sensitivity analysis with special focus on the eutrophying emissions was carried out by evaluating the amount of laccase and lignin based phenolic material used. The combined reduction in both bonding agents may slightly reduce the contributions to this impact category. In addition, a hypothetical scenario with no laccase and with a higher concentration of the lignin based material (25% more) could improve the environmental profile in all impact categories with a reduction of 1.5% in EP.Further research should focus mainly on laccase production, in order to reduce its energy demand as well as on the amount of green adhesive required to obtain mechanical and swelling properties similar to those of conventional hardboard.