Bound residues: environmental solution or future problem?

The paper examines the issue of bound residues from the viewpoint of the risk assessment procedures employed for environmental protection. It considers, on one hand, the evidence that such residues are so tightly bound to soil organic matter as to be essentially unavailable; and on the other, the perspective that we should not be loading up the environment with compounds whose future behaviour and release we cannot predict. Existing knowledge of the mechanisms by which residues bind to soil organic matter suggests that release will be closely dependent on soil organic matter breakdown. Simple models of organic matter turnover suggest that the release following single applications of individual compounds will be very slow; but the significance of releases following repeated application over many years of a number of compounds needs to be investigated further. Applying environmental risk assessment techniques is complicated by the difficulty in identifying parent molecules and potential metabolites in the bound residue fraction. The paper concludes that for single additions of individual compounds, bound residues probably do represent an environmental solution. But the long-term significance of bound residues formed from multiple additions of a number of compounds is less clear. The paper recommends that future work should emphasise the biological significance of such residues and their release.     

Plant protection products: assessing the risk for terrestrial plants

The fundamental data requirements for the authorization of plant protection products and the inclusion of active ingredients in Annex I of Council Directive 91/414/EEC (Council Directive of 15 July 1991 referring to placing plant protection products on the market (91/414/EEC). Official Journal of European Communities L 230, 19 August 1991) are described in the Annexes II and III of this Directive. Definite instructions with regard to preconditions for implementation and methodology (guidelines) concerning investigations with terrestrial plants are deficient. In addition to that, the uniform principles for the registration of plant protection products in the Member States described in Annex VI of the directive do not include any criteria concerning the risk assessment for non-target plants. However, plant protection products often show effects on non-target plants which need to be assessed as a requirement for the authorisation of the product. Hence, the German Federal Environmental Agency has developed a tiered approach to assess the effects of plant protection products on non-terrestrial plants. The risk is assessed using the effect-concentration evaluated in ecotoxicological tests and the environmental concentration predicted by validated exposure models. To protect non-target plants in terrestrial ecosystems assessment factors need to be considered. In the future, the risk for terrestrial plants needs to be addressed, also with regard to the revision of the Annexes of Directive 91/414/EEC.     

土壤轻组有机质

轻组有机质主要是由不同分解程度的植物残体和一些微生物结构体组成,它的改变可以用来指示土壤肥力的变化.本文综述了轻组的分离方法、轻组的组成、种植和施肥对轻组的影响、轻组在土壤团聚体和土壤剖面中的分布以及轻组的季节性变化.     

Monometal and competitive adsorption of heavy metals by sewage sludge-amended soil

Sewage sludge-amended soils may alter their ability to adsorb heavy metals over time, due to the decomposition of sludge-borne organic matter. Thus, we studied Cd, Ni, and Zn adsorption by a sewage sludge-amended soil (Typic Xerofluvent) before and after one-year incubation in both monometal and competitive systems. In the monometal system, the order of decreasing sorption was Zn>Cd>Ni. Competition significantly reduced metal K(d), especially that of Cd which decreased by nearly 50%. Over the course of the incubation there was a 31% reduction of soil organic matter content. At the same time, in competitive systems Cd K(d) significantly decreased, while Zn K(d) significantly increased, and Ni K(d) remained unaffected. This study shows that sewage sludge-amended soils may change in their ability to sorb heavy metals over time at high metal concentrations. The data suggest that Cd is likely to be of most environmental significance in such soils, since it exhibited decreased sorption under competitive conditions and as the organic matter content of the soil was reduced. The potential for long-term release of metals should be considered in the risk assessment associated with sewage sludge addition to soils, particularly in climates where degradation of organic matter is likely to be enhanced.     

Human health and environmental risk assessment: the need for a more harmonised and integrated approach

Historically the procedures for human risk assessment and for risk assessment have developed separately with different terminologies and separate data bases. The identification that there are many common features and that sharing of certain types of data for risk assessment purposes would be beneficial is a driver towards a better integration of their procedures. Risk assessors are facing increasing challenges from governments, stimulated by public pressure for (i) human and environmental risk assessments of an ever growing number of products and processes, (ii) further restrictions of the use of animal tests and human studies on ethical grounds, (iii) the requirement to demonstrate that the assessments are independent, transparent and of high quality, (iv) reducing resources in particular a diminishing number of individuals with the scientific depth, breadth and independence act as risk assessors, (v) the need to incorporate new sciences continually and new discoveries into the risk assessment process. It is important for society that these challenges are met successfully. This requires changes in both risk assessment procedures and in the infrastructure needed to support them. Risk assessment is a science based process for establishing the likelihood of adverse effects to human health and to the environment from specific chemical, biological and physical agents. In the last few years there has been a renewed effort, by international bodies such as WHO, OECD and the EU, to achieve a more integrated and harmonised approach to risk assessment. Before examining the potential for a more integrated approach to risk assessment it is timely to consider the key factors which have led to the current position.     

Germination and seedling growth of the water cress Rorippa sp. exposed to the chelant [S,S]-EDDS

With the implementation of the new EU environmental framework directives, high tier risk assessments of chemicals will be increasingly needed. For high production chemicals, additional tests will complement the standard battery for aquatic toxicity assessments (daphnids, algae, and fish). In the context of a new chemical notification at the European Union level, we have developed a seed germination and root elongation toxicity test with the freshwater aquatic plant Rorippa nasturtium-aquaticum (water cress) to confirm the low environmental risk of the chelant [S,S]-EDDS. A 14 day semi-static growth inhibition test was conducted with daily renewal of the test solution. No concentration related inhibition was found on the basis of any of the criteria investigated, i.e., time and extent of germination, biomass, number of leaves, stalk and root lengths. The no-observed effect concentration was considered to be >or=387 mg SS-EDDS/l. Although germination was selected as an appropriate endpoint to assess the effect of a chelant on an aquatic plant (other endpoints would have been dependant on essential metals that are chelated in standard culture tests), the absence of dose related effects requires further tests with higher exposure concentrations and/or other toxicant(s) to assess the validity of the test as a general tool for aquatic risk assessment.     

Effects of the organic matter from swine wastewater on the adsorption and desorption of alachlor in soil

The application of swine wastewater to the soil for agricultural purposes results in the addition of total and dissolved organic matter to the soil, which may interfere with the dynamics of pesticides in the soil. The objective of this study was to evaluate the effects of the application of total and dissolved organic matter from a biodigester and a treatment lagoon of swine wastewater in the adsorption and desorption of alachlor [2-chloro-2,6-diethyl-N(methoxymethyl acetamide)]. The assay was performed by the batch equilibrium method, and the results were fitted to the Freundlich model. The curve comparison test revealed a greater adsorption of alachlor in the soil treated with swine wastewater from the biodigester. The adsorption and desorption of alachlor increased in the soils where swine wastewater was added, and hysteresis was observed in all of the treatments.     

Effects of the organic matter from swine wastewater on the adsorption and desorption of alachlor in soil

The application of swine wastewater to the soil for agricultural purposes results in the addition of total and dissolved organic matter to the soil, which may interfere with the dynamics of pesticides in the soil. The objective of this study was to evaluate the effects of the application of total and dissolved organic matter from a biodigester and a treatment lagoon of swine wastewater in the adsorption and desorption of alachlor [2-chloro-2,6-diethyl-N(methoxymethyl acetamide)]. The assay was performed by the batch equilibrium method, and the results were fitted to the Freundlich model. The curve comparison test revealed a greater adsorption of alachlor in the soil treated with swine wastewater from the biodigester. The adsorption and desorption of alachlor increased in the soils where swine wastewater was added, and hysteresis was observed in all of the treatments.     

Can varying concepts of susceptibility in risk assessment affect particulate matter standards?

The Clean Air Act mandates that sensitive subpopulations be considered in setting standards to protect the public's health. The purposes of this paper are to point out different conceptualizations of susceptibility, examine how it is approached in risk-related processes, and recommend ways it may be more explicitly framed for risk assessment and management purposes. We studied the traditional risk assessment paradigm, the U.S. Environmental Protection Agency (EPA) guidelines and revised PM standard, discussions from recent interdisciplinary meetings, and peer-reviewed literature. Areas of controversy include what factors intrinsic and extrinsic to the host should be incorporated in susceptibility, what health endpoints are of concern, whether susceptibility is deterministic or stochastic, and whether it should be defined on an individual or population scale. Recent discussions about susceptibility applied to PM indicate that it needs to be more clearly defined and evaluated for scientific and policy purposes. We conclude that varying concepts of susceptibility can affect risk-related processes such as PM standard setting. We recommend that susceptibility be clearly defined in the problem statement of risk assessments and be addressed in a specific subsection of risk characterization, integrating all susceptibility findings from the prior three steps in the risk assessment paradigm.     

Metal/metalloid fixation by litter during decomposition affected by silicon availability during plant growth

Organic matter is known to accumulate high amounts of metals/metalloids, enhanced during the process of decomposition by heterotrophic biofilms (with high fixation capacity for metals/metalloids). The colonization by microbes and the decay rate of the organic matter depends on different litter properties. Main litter properties affecting the decomposition of organic matter such as the nutrient ratios and the content of cellulose, lignin and phenols are currently described to be changed by silicon availability. But less is known about the impact of silicon availability during plant growth on elemental fixation during decay. Hence, this research focuses on the impact of silicon availability during plant growth on fixation of 42 elements during litter decay, by controlling the litter properties. The results of this experiment are a significantly higher metal/metalloid accumulation during decomposition of plant litter grown under low silicon availability. This may be explained by the altered litter properties (mainly nutrient content) affecting the microbial decomposition of the litter, the microbial growth on the litter and possibly by the silicon double layer, which is evident in leaf litter with high silicon content and reduces the binding sites for metals/metalloids. Furthermore, this silicon double layer may also reduce the growing biofilm by reducing the availability of carbon compounds at the litter surface and has to be elucidated in further research. Hence, low silicon availability during plant growth enhances the metal/metalloid accumulation into plant litter during aquatic decomposition.     

Dynamics of trace metals in organisms and ecosystems: prediction of metal bioconcentration in different organisms and estimation of exposure risks

Metal ions interact with biological materials and their decomposition products by ligation (coordination complex-formation with certain moieties containing O, N, S, etc.). The extent of this interaction depends on the identities of both ligand and metal ion and can be described by some equation derived from perturbation theory. Uptake of metal ions - including highly toxic ones - from soils is controlled by a competition between root exudate components and soil organic matter (SOM) for the ions. SOM consists of a variety of potential ligands which evolve during humification towards more efficient binding (retention) of metals such as Cu, Ni, Cr but also of toxicants like U, Cd. The actual way of interaction can be inferred from stoichiometry of the involved compounds and the C/N ratio in the soil, providing predictions as to which metals will be most efficiently shuttled into green plants or fungi, respectively. The latter, selective process is crucial for closing nutrient cycles and sensitively depends on C/N ratio and the extent of "forcing" by onfalling leaf or needle litter. Therefore, analytical data on the soil can be used to predict possible risks of exposition to toxic metals also for human consumption of plant parts.     

Long-term effects of aided phytostabilisation of trace elements on microbial biomass and activity, enzyme activities, and composition of microbial community in the Jales contaminated mine spoils

We studied the effectiveness of remediation on microbial endpoints, namely microbial biomass and activity, microbial and plant species richness, of an As-contaminated mine spoil, amended with compost (C) alone and in combination with beringite (B) or zerovalent iron grit (Z), to increase organic matter content and reduce trace elements mobility, and to allow Holcus lanatus and Pinus pinaster growth. Untreated spoil showed the lowest microbial biomass and activity and hydrolase activities, and H. lanatus as sole plant species, whereas the presented aided phytostabilisation option, especially CBZ treatment, significantly increased microbial biomass and activity and allowed colonisation by several plant species, comparable to those of an uncontaminated sandy soil. Microbial species richness was only increased in spoils amended with C alone. No clear correlation occurred between trace element mobility and microbial parameters and plant species richness. Our results indicate that the choice of indicators of soil remediation practices is a bottleneck.     

Comparing growth development of <Emphasis Type="Italic">Myriophyllum</Emphasis> spp. in laboratory and field experiments for ecotoxicological testing

BACKGROUND, GOALS AND SCOPE: Risk assessment of herbicides and the evaluation of contaminated sediments based on algae and the macrophyte Lemna sp. alone may underestimate the potential hazard of certain compounds. Therefore, various test systems with Myriophyllum spp. have been developed recently to assess the phytotoxicity in surface waters and natural sediments. In the present study, experiments investigating the growth development of Myriophyllum spp. were performed in the laboratory under defined conditions and in mesocosms under environmentally realistic exposure conditions to evaluate the suitability of these species as potential standard test organisms in ecotoxicological testing. This study provides data on the endpoints biomass, plant length and root development. MATERIALS AND METHODS: Six independent experiments were performed to investigate the plant development of Myriophyllum spp. under control conditions. The main difference in the experiments was the complexity of the test systems ranging from simple laboratory experiments to complex outdoor mesocosm studies. At the start of each experiment, uniform cuttings of Myriophyllum spp. were placed in vessels with or without sediments to reduce variability between replicates. The endpoints considered in this investigation were biomass (fresh weight of the whole plant), length of the main shoot, length of the side shoots, total length of the plant (calculated from the length of the main and side shoots) and root formation. Root to shoot ratios were calculated as a further measure for plant development. Relative growth rates (RGR) based on plant length (RG(L)R) and on biomass (RG(B)R) were calculated. RESULTS: Despite the various experimental conditions, comparable growth was obtained in all test systems and the variability of endpoints, such as total length and biomass of plants, was low. It was observed that the RGR of M. spicatum in the simple laboratory test system with sediment were comparable to growth data obtained for M. verticillatum and M. spicatum grown in indoor and outdoor mesocosms, thus indicating that Myriophyllum growth tends to increase by the addition of sediment. High variability was determined for the endpoints length of the side shoots, total root length and biomass of roots. DISCUSSION: One challenge for a test design to investigate phytotoxicity on aquatic plants is to obtain good growth of the plants. From the results, it can be concluded that the experimental conditions in the various test systems were suitable to study the plant development of Myriophyllum spp. because obtained growth rates were comparable between laboratory and field investigations. Another challenge for developing a plant biotest system is the definition of sensitive endpoints. Low variability is preferred to detect minor effects of chemicals or polluted sediments on plant development. In our studies, the variability of the endpoints biomass and total length of plant was low and, therefore, they have much potential as endpoints for assessing toxicity. CONCLUSIONS: The methodologies presented in this study have applications within the risk assessment for aquatic plants and have the advantage of assessing effects taking into account the relevant exposure pathways via water and/or sediment for compounds under investigation. RECOMMENDATIONS AND PERSPECTIVES: Setting safe quality criteria for surface water and sediments is one of the challenges authorities are facing today. Myriophyllum spp. is recommended as suitable test species to investigate phytotoxicity in surface water and sediments. These results, thus, might serve as a basis for the compilation of a new harmonised guideline for ecotoxicological testing with aquatic macrophytes.     

Can Varying Concepts of Susceptibility in Risk Assessment Affect Particulate Matter Standards?

ABSTRACT

The Clean Air Act mandates that sensitive subpopulations be considered in setting standards to protect the public's health. The purposes of this paper are to point out different conceptualizations of susceptibility, examine how it is approached in risk-related processes, and recommend ways it may be more explicitly framed for risk assessment and management purposes. We studied the traditional risk assessment paradigm, the U.S. Environmental Protection Agency (EPA) guidelines and revised PM standard, discussions from recent interdisciplinary meetings, and peer-reviewed literature. Areas of controversy include what factors intrinsic and extrinsic to the host should be incorporated in susceptibility, what health endpoints are of concern, whether susceptibility is deterministic or stochastic, and whether it should be defined on an individual or population scale. Recent discussions about susceptibility applied to PM indicate that it needs to be more clearly defined and evaluated for scientific and policy purposes. We conclude that varying concepts of susceptibility can affect risk-related processes such as PM standard setting. We recommend that susceptibility be clearly defined in the problem statement of risk assessments and be addressed in a specific subsection of risk characterization, integrating all susceptibility findings from the prior three     

Organically bound halogens in coniferous forest soil -Distribution pattern and evidence of in situ production

We examined organically bound halogens in a coniferous soil profile and in Norway spruce litter enclosed in litter bags and subjected to degradation in field. Throughout the soil profile the total amount of organically bound halogens (TOX, μg Cl/g soil) was related to organic matter, i.e. amounts decreased with increasing depth. In contrast, the organic chlorine to organic carbon ratio (mg Cl_org:g C_org) increased with increasing depth, and a pronounced increase in this ratio was observed in the transition between the O-horizon and the A-horizon, strongly indicating that in situ production of organically bound halogens occur in soil. This conclusion was strengtened by the results of the litter bag study, which clearly showed that a net-production of organically bound halogens occurred during decomposition of the spruce needle litter. Furthermore, this part of the study showed that organically bound halogens are not a static factor of organic matter. On the contrary, the results strongly indicated that during decomposition of organic matter, organically bound halogens are subjected to both production, i.e. incorporation of inorganic halides into organic matter, and mineralisation, i.e. release of inorganic halides from organic matter. A method previously developed in our laboratory to determine TOX in soil was further evaluated; there were no indications that inorganic halides interfere with the determination.     

A comparison of rate-response toxicity tests with Aphidius rhopalosiphi (Hymenoptera: Aphidiidae) using glass,leaves and whole plants as substrate

Rate-response toxicity tests on Aphidius rhopalosiphi were carried out with seven plant protection products using three different test systems. The first type of test system conformed to the standard laboratory testing guidelines and consisted of two treated glass plates fitted into a metal frame, which created an enclosure for the wasps. In the second type of test system, the plant protection products were applied to two bean-leaf disks mounted on agar filled dishes, which were fitted to a transparent plastic frame. The third type of test system consisted of potted barley plants, which were treated and covered with an acrylic cylinder. Adult wasps were exposed to the dried residues of the products for 48 h before wasp mortality was assessed. For each product and test system, the LR50 value (application rate at which 50% mortality of the wasps occurs) was determined with a Bayesian Probit analysis. Technically, rate-response testing was feasible with all three test systems, and rate-response relationships could be established. The results support a sequential testing scheme, as the LR50 values increased from 'glass plate test' to 'excised leaf test' to 'whole plant test' with all tested products. The LR50 values were 7.8-340 times higher on whole plants than on glass plates. Because of the variability of this factor, a numerical safety factor cannot be used to substitute extended laboratory testing for regulatory purposes.     

Evaluation of EU risk assessments existing chemicals (EC Regulation 793/93)

An evaluation was performed on the first group (41) of completed risk assessments for chemicals of the EU priority lists (Existing Chemicals; EC Regulation 793/93). The evaluation focussed on the conclusions of the risk assessments. The EU risk assessment process detected a high number of substances of concern. Furthermore priority chemicals may pose potential risks to the whole range of protection goals of the risk assessment. The predictability of the risk assessments for priority chemicals was investigated. Our a priori knowledge on possible risks of priority chemicals is found to be poor, especially for consumers. Both for environment and human health the potential risks were linked with a broad spectrum of use patterns. It is concluded that no industry category can in advance be excluded from performing risk assessments. For a great number of chemicals, additional testing was found to be needed to finalize the risk assessment. This evokes questions about the completeness of the current base-set, but also about the suitability of some of the submitted human health tests that should initially fulfil the base-set needs. The results of this evaluation are useful for ongoing discussions on risk assessment processes for chemicals.     

Mobility of metals and metalloids in a multi-element contaminated soil 20 years after cessation of the pollution source activity

Knowledge of trace element concentrations and mobility is important in the ecotoxicological assessment of contaminated soils. We analysed soil pore water under field conditions to provide new insights into the mobility of residual contaminants in the surface 50cm of a highly contaminated woodland soil. Cadmium and Zn were highly mobile in the acidic soil, concentrations increasing with depth in soil pore water, showing considerable downward mobility. High levels of surface organic matter restricted the solubility of Cu, Pb and Sb, with highest concentrations being found close to the surface. Dissolved organic carbon in pore water had a strong influence on mobility of Cu, Zn, Pb and Sb. Elevated As had moved from the organic surface horizons but was largely immobilised in deeper layers and associated with Fe and Al oxides. The measured differential mobility of pollutants in the present study is highly relevant to protection of groundwater and other receptors.     

Speciation of zinc in contaminated soils

The chemical speciation of zinc in soil solutions is critical to the understanding of its bioavailability and potential toxic effects. We studied the speciation of Zn in soil solution extracts from 66 contaminated soils representative of a wide range of field conditions in both North America and Europe. Within this dataset, we evaluated the links among the dissolved concentrations of zinc and the speciation of Zn(2+), soil solution pH, total soil Zn, dissolved organic matter (DOM), soil organic matter (SOM) and the concentrations of different inorganic anions. The solid-liquid partitioning coefficient (K(d)) for Zn ranged from 17 to 13,100Lkg(-1) soil. The fraction of dissolved Zn bound to DOM varied from 60% to 98% and the soil solution free Zn(2+) varied from 40% to 60% of the labile Zn. Multiple regression equations to predict free Zn(2+), dissolved Zn and the solid-liquid partitioning of Zn are given for potential use in environmental fate modeling and risk assessment. The multiple regressions also highlight some of the most important soil properties controlling the solubility and chemical speciation of zinc in contaminated soils.