Cadmium solubility and sorption in a long-term sludge-amended arable soil

Cadmium solubility and sorption in an arable clay loam soil that had received sewage sludge for 41 years were compared to an unsludged control in batch studies. Soil pH dominated Cd sorption, explaining >92% of the variation in Kd values in both treatments. At any pH, Cd sorption was apparently slightly but significantly (p < 0.05) smaller in the sludge-amended soil compared to the control, even though the organic carbon content was 70% larger and the ammonium oxalate-extractable iron content was roughly doubled. Correction for dissolved organic carbon (DOC) complexation with the speciation model WHAM reduced the difference in sorption between treatments, but the sludged soil still had significantly smaller Kd values (p < 0.01). Batch equilibrations without addition of Cd showed that there was no significant difference in the solubility of "native" cadmium (defined as EDTA-extractable Cd) in sludged and control soils. The reason for the lack of increase in Cd sorption in the sludge-amended soil has not been established, but it may be due to competition for sorption sites on humic compounds with sludge-derived Fe and trace metals such as zinc. The fact that the pyrophosphate-extractable (i.e., organically associated) iron content was seven times larger in the sludged soil provides some supporting evidence for this hypothesis.     

Modeling organic carbon dynamics and cadmium fate in long-term sludge-amended soil

A model is described that may help to resolve uncertainty and controversy over the long-term consequences of sludge applications to arable land, especially with regard to the effects of sludge adsorption characteristics on trace metal solubility and bioavailability (e.g., the sludge "time bomb" or sludge "protection" hypotheses). Mass balances of organic and inorganic material derived from sludge and crop residues are simulated. Each pool has a potentially different adsorption affinity for trace metals, and this leads to changes in the adsorption capacity of sludge-amended soil that influence leaching and crop uptake. Model simulations were compared with measured changes in organic carbon and ethylenediaminetetraacetic acid (EDTA)-extractable cadmium contents in a clay loam soil following 41 years of sludge applications. The model adequately reproduced the data, although discrepancies in the vertical distribution of Cd were attributed to the effects of macropore transport and root-uptake driven recirculation. A Monte Carlo sensitivity analysis demonstrated that the most important parameters affecting leaching and crop uptake were the Cd loading and parameters controlling adsorption, especially the partition coefficient for sludge-derived inorganic material and the exponent regulating the effect of pH on sorption. Scenario simulations show that no general conclusions can be drawn with respect to the validity of the sludge "time bomb" and sludge "protection" hypotheses. Either may occur, or neither, depending on three key system parameters: the ratio of sludge adsorption capacity to the initial adsorption capacity of the soil, the proportion of the sludge adsorption capacity contributed by the inorganic fraction, and the sludge Cd loading.     

Changing of Lead and Cadmium Pools of Swedish Forest Soils

The aims of the paper are to; i)evaluate the rate and direction of present changesin lead (Pb) and cadmium (Cd) soil pools of Swedishforests; ii) discuss processes of importance forleaching of Pb and Cd in Swedish forest soils. Thepresently ongoing changes of Pb and Cd pools ofSwedish forest soils are evaluated by compilationof data from the literature and unpublishedsources. It is concluded that Cd pools arepresently decreasing in larger areas of Sweden. Therate of decrease is mainly determined by soilacidity status; Cd leaching is regulated by ionexchange with Ca²⁺, Mg²⁺, Al³⁺ andH⁺, and is higher in acid soils. The Pb poolsare presently increasing with 0.1 to 0.3 percentannually in the soil down to 0.5 meter. Pb isredistributed from the O horizon to the B horizon,most pronounced in spruce forests; the Pb pools ofthe O horizon are presently not increasing, but isslightly decreasing by 0.1 to 0.2 percent annually. The leaching of Pb in the soil is controlled byfactors regulating the solubility of organicmatter.     

Environmental assessment of plant protection strategies using scenarios for pig feed production

Two scenarios for future pig meat production were constructed. The first was a "business as usual" scenario, where the pig feed was based on domestic grain and imported soy-meal, and no efforts were made to reduce pesticide use. The second scenario had a strong environmental focus, and both peas and rapeseed were grown at pig-farm level to produce grain and protein feed. Preventive measures, such as a more diverse crop rotation and mechanical weed control, were combined to reduce pesticide use. The two scenarios were environmentally assessed by Life Cycle Assessment (LCA) and a pesticide risk indicator model (PRI-Farm). The results showed environmentally sound possibilities to reduce pesticide dependency and risks by using altered plant protection strategies in pig-feed production. Organizing on-farm feed production so that protein feed crops are integrated with grain crops contributes to a more diverse crop rotation.     

Occurrence and levels of organochlorine compounds in human breast milk in Bangladesh

In low-income countries, the use of some organochlorine pesticides is still common in order to increase food production. Monitoring the chemical exposure is an important step in risk-reducing strategies. This is the first study to report concentrations of organochlorines in breast milk of women from Bangladesh where farming is the main income source.Organochlorines such as p,p′-DDT, o,p′-DDT, p,p′-DDE, p,p′-DDD (i.e., ∑DDT), HCB, α-, β- and γ-HCH, trans-chlordane, cis-chlordane, oxy-chlordane, trans-nonachlor, cis-nonachlor, mirex and polychlorinated biphenyls (CB 28, 52, 99, 101, 105, 114, 118, 123, 128, 138, 141, 149, 153, 156, 157, 163, 167, 170, 180, 183, 187, 189, 194) were analyzed in breast milk collected in 2002 from 72 first-time mothers (median age 20 years) living in the rural area Matlab, Bangladesh.While the concentrations of PCBs and many of the pesticides were low, the concentrations of p,p′-DDT and its metabolite p,p′-DDE were high (median 349 and 1645 ng g⁻¹ lipid, respectively) in comparison to other countries. The median value of ∑DDT was 2123 ng g⁻¹ lipid. The estimated daily exposure to p,p′-DDT, p,p′-DDE and ∑DDTs was 10, 30 and 42 μg kg⁻¹ body weight, respectively, in 3 months old infants. The p,p′-DDE/p,p′-DDT ratio ranged from 1 to 23, where 58% of the mothers had a ratio below 5 indicating recent or ongoing DDT exposure.This study reports infant exposure and maternal body burden of organochlorines through breast milk. Although the findings give no reason to limit breast-feeding, it is essential to identify the main exposure sources and find means to decrease the exposure.     

应用猪饲料生产情景分析法的植物保护策略环境评价

对未来的猪肉生产构建了两种情景.一种是"基型"(即一切照旧)(business as usual)情景,这一情景中,猪饲料是以国内生产的谷谷和进口的豆饼为基本原料,未努力减少农药的用量.第二种情景更多的关注环境,在猪场还种植豌豆和油菜用以提供谷物和蛋白质饲料.采用更多种不同作物的轮作和机械除草相结合来降低农药的用量,以达到降低环境污染的目的.这两种情景同时用两种方法进行环境评估:生命周期评价法(LCA)(Life cycle Assessment)和农药风险指标模型(PRI-Farm)(Pesticide risk indicator model).结论表明:在猪饲料生产中通过运用改变作物的保护策略以期降低农药的用量和减小其风险是环保可行的.组织起农场的饲料生产,使蛋白质饲料和谷物生产相结合可促成更多种作物的轮作.