Elutriate testing

As a result, the concept of toxicity classes and management categories linked to dredged-material relocation, as presented in Tables 2 and 3, are presently based on sediment porewater and elutriate testing and may have to be adjusted in the long term. Incorporation of solid-phase tests in routine test batteries should also serve to improve sediment quality guidelines and ensure better protection of aquatic ecosystems. 

Figure 10.4 represents a summary of bioassays distinguishing between whole soil and elutriate tests reflecting different assessment objectives. Whilst whole soil tests may preferably be used for ecological assessments (e.g. the investigation of habitat functions of soil), testing of elutriates provides information on the mobility of contaminants and the retention capability of soil. 

Figure 5-3 Partition of Cadmium in Anoxic Mud from Hamburg Harbor in Relation to the Pretreatment Procedures (Kersten et al., 1985) (A) Control Extracted as Received Under Oxygen-Free Conditions (B) After Treatment with Elutriate Test ...

One approach to increase certainty of data has been suggested e.g. by Suter (1983) the use of several lines of evidence in order to make a best-judgement weight of evidence decision. In this context, the application of different biotests with different endpoints, exposure routes and sensitivities towards contaminants could be regarded as different lines of evidence. If such a biotest battery, however, comprises e.g. sediment contact tests as well as elutriate tests, additional information could be drawn from the results on whether potential risks of contaminants are sediment-focused or could also affect organisms in tlie water column upon resuspension. 

Liss, W. and Ahlf, W. (1997) Evidence from whole-sediment, porewater, and elutriate testing in toxicity assessment of contaminated sediments, Ecotoxicol. Environ. Safety, 36, pp. 140-147. 

The advantage of short-term elutriate tests is that especially important parameters can be directly observed and particularly unfavorable conditions can be simulated interpretation may become difficult for systems undergoing redox variations, which is usually the case both in aquatic sediments and land-disposed dredged materials. 

Gravitational Methods GONELL AIR ELUTRIATOR. This is the prototype of all analytical separators with laminar air flow. It consists of a cylindrical brass tube (or a series of tubes) with a conical base. An air inlet is provided in this base on the axis of the tube. The sample of powder is placed in the inlet cone, and air is blown thru the largest tube until separation is deemed complete, or for specified periods of time. The residue is removed, weighed, and transferred to a smaller diameter tube, and the test is repeated. The tube should have polished internal surfaces and should be periodically tapped or vibrated to disturb settled powder... 

A lot of attempts have been made to describe the time dependence of the attrition rate in batch fluidized bed processes. Gwyn (1969) studied the degradation of catalysts in a small-scale test apparatus and defined the elutriated particles as the only attrition product. He described the increase of the elutriated mass, Wel, with time, t, based on the initial solid bed mass, Wbed 0, by the now widely known Gwyn equation ... 

Both washed and unwashed cottons were processed through a blender feeder, a No. 12 horizontal opener, and a two-beater picker and made into picker laps. The carding was conducted in our model cardroom at 18,2 kg/h, and dust levels were determined by use of vertical elutriators. The cottons were spun into 19.7 mg/ m yarn of 38.2 twist factor at 13000 rpm spindle speed in a 4536 spindle-hour test. 

The alternative Instrument used was a Portable Continuous Aerosol Monitor (PCAM) manufactured by ppm, Inc., and dust concentrations measured with the PCAM were 5-15% lower than values obtained with standard vertical elutriators. Calculations and examples for TWA exposures, equivalency tests, and vertical elutriator coefficients of variation are included. 

Cotton dust sampling is a plant site test, normally involving unsophisticated field equipment, ever-changing plant conditions, and technician-level labor in performing many functions. However, with adequate equipment and attention to technique, we have found that good quality data can be obtained for each survey. The purpose of this paper is to share with you some of the instrumentation, equipment modifications and techniques we have studied and employed to obtain vertical elutriator (VE) data with average coefficients of variation less than 10%. 

Figure 9. Schematic of PC AM equivalency testing rig showing the relationship of large vertical elutriators to PC AM small vertical elutriator.

Evaluations of various soil and sediment samplers have been reported [56, 57]. The sediment shovel proved highly practical, but was limited because small particles tend to be lost when the shovel is lifted [56]. A cryogenic sediment sampler was less convenient to use, but allowed the collection of almost undisturbed samples. Houba described a different device for the automatic subsampling of soil, sediment and plant material for proficiency testing [57]. In another study, Thoms showed that freeze-sampling collects representative sediment samples, whereas grab-sampling introduces a bias into the textural composition of the 120 mesh fraction, due to washout and elutriation of the finer fractions [58]. 

Hauser, B., Schrader, G. and Bahadir, M. (1997) Comparison of acute toxicity and genotoxic concentrations of single compounds and waste elutriates using the Microtox/Mutatox test system, Ecotoxicology and Environmental Safety 38 (3), 227-231. 

Although this chapter focuses on applications with effluent wastewaters, all types of aquatic environmental media (freshwater, brackish, marine) can be appraised with the pT-scale procedure. Testing of liquid samples is virtually unlimited and can include untreated and treated wastewater, surface water, ground water, porewater, elutriates and organic extracts of sediments. Applications could also be extended to assess toxicity of particle-bound substances in suspended matter and sediments. In this case, sample dilutions can be made with reference sediment material (Hoss and Krebs, 2003). The pT-method can also capture the effects of both soluble and particulate toxicity in a sample, provided that appropriate bioassays are employed. 

The general objective, principle, and scope of application of the pT-method are succinctly described in Section 1 and also reported elsewhere in this book (see Chapter 3 of this volume, Section 5.1), where readers will appreciate that this hazard assessment scheme is adaptable to both liquid and solid media. Briefly recalled here in the context of solid-media samples such as dredged material, the pT-value, which relates to a single bioassay, and the pT-index, derived from the most sensitive organism in a test battery, permit a numerical classification of environmental samples on the basis of ecotoxicological principles. Sediment from any aquatic ecosystem (freshwater, brackish, marine) and from any of its phases (whole sediment, porewaters, elutriates or organic extracts) can be appraised provided that the proper standardized toxicity tests are available. There are whole-sediment test protocols standardized for many agencies (e.g., Environment Canada, ASTM). 

In the case of whole-sediment toxicity determination, the necessary dilutions can be made with reference sediment material. A standardized method whereby polluted sediments can be diluted with unpolluted sediments for sediment-contact tests is currently being researched (Hoss and Krebs, 2003). Hence, the pT-method is capable of capturing the toxic effects of both soluble and adsorbed contaminants in a given sample, assuming that appropriate toxicity tests (i.e., solid-phase contact tests on whole sediment and tests on porewater or elutriates) are used. 

Appraising the toxic potential of biologically available contaminants in sediment should include three compartments the whole sediment (with standardized direct contact assays when these are available), the porewater, and the elutriate (aqueous extract). Additional hazard information can also be obtained from toxicity testing conducted on organic extracts using methanol or acetone. 

---