Chemical Pollutants in Air, Water, Soil, and Solid Wastes Phần 5 ppt

PHENOLS Phenols are or ganic compounds containing an –OH group attached to an aromatic ring. The structure of phenol, the prototype compound of this class, is Although the presence of other substituents in the ring can produce an array of diverse compounds of entirely different properties, the chemical analysis of most phenols, however, can be performed in the same way. This is attributed to (1) the acidic nature of the phenolic –OH group, and (2) that the –OH group can form derivatives. Trace amounts of phenols may occur in many natural waters as well as in domestic and industrial wastewaters. Chlorination of such waters can produce chlorophenols. Several phenolic compounds occurring in industrial wastewaters, soils, sed- iments, and hazardous wastes are classified as U.S. EPA priority pollutants. These are presented in Table 2.23.1. The total phenolic compounds in an aqueous sample can be determined by a colorimetric method using 4-aminoantipyrine. This reagent reacts with phenolic compounds at pH 8 in the presence of potassium ferricyanide to form a colored antipyrine dye, the absorbance of which is measured at 500 nm. The antipyrine dye may also be extracted from the aqueous solution by chloroform. The absor - bance of the chloroform extract is measured at 460 nm. The sample may be distilled before analysis for the removal of interfering nonvolatile compounds. The above colorimetric method determines only ortho- and meta-substituted phenols and not all phenols. When the pH is properly adjusted, certain para- substituted phenols, which include methoxyl-, halogen-, carboxyl-, and sulfonic acid substituents, may be analyzed too. OH 2.23 © 1997 by CRC Press LLC © 1997 by CRC Press LLC PHOSPHORUS Phosphorus occurs in natural waters, wastewaters, sediments, and sludges. The main sources of phosphorus released into the environment include fertilizers, many detergents and cleaning preparations, and boiler waters to which phosphates are added for treatment. From an analytical standpoint, phosphorus is classified into three main categories: 1. Orthophosphate, PO 4 3– , e.g., Na 3 PO 4 2. Condensed phosphate including meta-, pyro-, and polyphosphates: Na 2 P 2 O 6 , Na 3 P 3 O 9 (metaphosphate) Na 4 P 2 O 7 (pyrophosphate) Na 5 P 3 O 10 (tripolyphosphate) 3. Organically bound phosphorus Orthophosphate and condensed phosphate are a measure of inorganic phos- phorus. The latter is also termed as “acid-hydrolyzable phosphate.” However, during mild acid hydrolysis, a small amount of phosphorus from organic phos- phorus compounds may be released. To determine suspended and dissolved forms of phosphorus, the sample should be filtered through a 0.45 μm membrane filter, and the filtrate and the residue analyzed separately. ANALYSIS The analytical steps are outlined in Figure 2.24.1. SAMPLE PREPARATION For the determination of acid-hydrolyzable phosphorus content of the sample, which is the difference between the orthophosphate in the untreated sample and the phosphate found after mild acid hydrolysis, the sample is first acidified with H 2 SO 4 and then hydrolyzed by boiling for 1.5 to 2 h. The sample may also be 2.24 © 1997 by CRC Press LLC PHTHALATE ESTERS Phthalates are the esters of phthalic acid having the following general structure: where R ′ and F ′′ are alkyl, alkenyl, and aryl groups. These substances are used as plasticizers of synthetic polymers such as polyvinyl chloride and cellulose acetate. Lower aliphatic phthalates are used in the manufacture of varnishes and insecticides. Many phthalates are found in trace quantities in wastewaters, soils, and hazardous wastes, often leaching out into the liquid stored in plastic containers or PVC bags. The acute toxicity of phthalates is very low, exhibiting symptoms of som- nolence and dyspnea in test animals only at high doses. Some of these substances are listed as U.S. EPA priority pollutants. Phthalates are analyzed by GC, LC, and GC/MS techniques after the extrac- tion and concentration of the samples. Aqueous samples may be directly analyzed by HPLC. Phthalates can be extracted from 1 L of aqueous sample by repeated extraction with methylene chloride using a separatory funnel. Phthalates having much greater solubility in methylene chloride, partition into this solvent and is separated. The extract is concentrated by boiling off methylene chloride and exchanged to hexane to a volume of 1 to 5 mL. Alternatively, 1 L aqueous sample is passed through a liquid-solid extraction cartridge containing octadecyl group bonded-silica. Phthalates adsorbed on the adsorbent surface are eluted with meth- ylene chloride. Phthalates in soils and other solid matrices may be extracted by sonication or Soxhlett extraction using methylene chloride. The extract is exchanged to hexane during concentration. If the extract is to be analyzed by GC/MS, the solvent exchange to hexane is not necessary and the methylene chloride extract may be directly injected. C COR′′ O OR′ O 2.25 © 1997 by CRC Press LLC © 1997 by CRC Press LLC To eliminate the interference effect of other contaminants and for dirty sample extracts, cleanup may become necessary. The extract is either passed through a florisil column or an alumina column and the phthalate esters are eluted with ether-hexane mixture (20% ethyl ether in hexane, v/v). The sample extract may be analyzed by GC or GC/MS. A 2- to 5- µ L aliquot of the extract is injected into a GC and the phthalates are detected by an electron capture detector, a flame ionization detector (FID), or a photoionization detector. Some of the chromatographic packed or capillary columns that may be used for the phthalate analysis are listed below: •Packed column: 1.5% SP-2250/1.96% SP-2401 on Supelcoport (100/120 mesh), 3% OV-1 on Supelcoport (100/120 mesh), and 3% SP-2100 on Supel- coport (100/120 mesh). • Capillary column: Fused silica capillary column containing 95% dimethyl polysiloxane and 5% diphenyl polysiloxane (e.g., 30 m, 0.53 mm ID, 1.5 µ m Rtx-5); 5% diphenyl polysiloxane, 94% dimethyl polysiloxane, and 1% vinyl polysiloxane (e.g., PTE-5, SPB-5, DB-5, or equivalent, 15 or 30 m × 0.53 mm ID). The column temperatures in the analysis may be maintained between 150° and 220°C. Benzyl benzoate or n -butyl benzoate may be used as internal standard. GC/MS analysis is a positive confirmatory test that identifies the compounds based on their characteristic ions. Table 2.25.1 lists the characteristic ions for some commonly occurring phthalates, which have been listed as U.S. EPA priority pollutants. Aqueous samples containing phthalates at concentrations higher than 10 ppm may be directly injected into GC and measured by FID. High performance liquid chromatography techniques may be successfully applied to analyze phthalate esters. A 15 or 25 cm column filled with 5 or 10 µ m silica-based packings is suitable. Short columns (3.3 cm × 4.6 mm), commonly called 3 × 3 columns, offer sufficient efficiency and reduce analysis time and solvent consumption. Phthalate esters resolve rapidly on a 3 × 3 Supelcosil LC-8 column (3 µ m packing) at 35°C and detected by a UV detector at 254 nm. Acetonitrile-water is used as mobile phase (flow rate: 2 ml/min; injection volume: 1 mL). Other equivalent columns under optimized conditions may be used. AIR ANALYSIS Analysis of phthalates in air may be performed by sampling 1 to 200 L air and collecting the esters over a 0.8 µ m cellulose ester membrane. The phthalates are desorbed with carbon disulfide and the eluant is injected into a GC equipped with an FID. A stainless steel column 2 m × 3 mm OD, containing 5% OV-101 on 100/120 Chromosorb W-HP was originally used in the development of this method (NIOSH Method 5020) for dibutyl phthalate and bis (2-ethylhexyl)phtha- late. Any other equivalent GC column listed above may also be used. The EPA Methods in Table 2.25.2 list only a specific number of phthalates. Any other phthalates not listed under the methods, however, may be analyzed using the same procedures. © 1997 by CRC Press LLC © 1997 by CRC Press LLC 240 POL YCHLORINATED BIPHENYLS (PCBS) Polychlorinated biphen yls (PCBs) are a class of chlorosubstituted biphenyl compounds that were once widely used as additives in transformer oils, lubricat- ing oils, and hydraulic fluids. These substances have high boiling points, exhib- iting high chemical and thermal stability, and flame resistance. However, because of their high toxicity and possible carcinogenic action in humans, these substances are no longer being used. In the U.S., PCBs were made under the trade name Aroclor. Table 2.26.1 presents the common Aroclors, their CAS numbers, and the chlorine contents. Each Aroclor is a mixture of several isomers. The general structure of the biphenyl ring is as follows: PCBs can be conveniently determined by most of the common analytical techniques which include GC-ECD, GC-HECD, GC-FID, GC/MS, HPLC, NMR, and enzyme immunoassay. Among these, GC-ECD and GC/MS are by far the most widely used techniques for the determination of PCBs in the environmental samples at a very low level of detection. While the former can detect the PCBs at subnanogram range, the mass selective detector (GC/MS) identifies the com- ponents relatively at a higher detection range, 10 to 50 times higher than the ECD detection level. GC/MS, however, is the best confirmatory method to positively confirm the presence of PCBs, especially in heavily contaminated samples. Aque- ous and nonaqueous samples must be extracted into a suitable solvent prior to their analysis. Being mixtures of several components, each Aroclor produces multiple peaks. The common GC columns that can readily separate the chlorobiphenyl components include 3% SP-2100, OV-1, DB-5, and SPB-5. Other equivalent columns or conditions can be used in the GC and GC/MS analyses. Table 2.26.2 presents some of the commonly used columns and conditions for analysis. 23 4 5 66′ 5′ 4′ 3′ 2′ 1′1 2.26 © 1997 by CRC Press LLC . column containing 95% dimethyl polysiloxane and 5% diphenyl polysiloxane (e.g., 30 m, 0 .53 mm ID, 1 .5 µ m Rtx -5) ; 5% diphenyl polysiloxane, 94% dimethyl polysiloxane, and 1% vinyl polysiloxane. vinyl polysiloxane (e.g., PTE -5, SPB -5, DB -5, or equivalent, 15 or 30 m × 0 .53 mm ID). The column temperatures in the analysis may be maintained between 150 ° and 220°C. Benzyl benzoate or. -dioxin rings, thus producing a total of 75 isomers. Chlorosub- stitution in positions 2, 3, 7, and 8 gives 2,3,7,8-tetrachlorodibenzo- p -dioxin (2,3,7,8-TCDD), CAS [1746-01-6], occurring in