Inhibitory effects of odor substances,geosmin and 2-methylisoborneol,on early development of sea urchins

Geosmin (1α,10β-dimethyl-9α-decanol) and 2-methylisoborneol ((1-R-exo)-1,2,7,7-tetramethyl-bicyclo-(2,2,1)-heptan-2-ol) (MIB) are volatile terpene derivatives, and have received a great deal of attention because they can cause musty/muddy off-flavor in water and food resources. By the Ames test, these metabolites showed no mutagenicity but antimicrobial activity toward tester strains. While these compounds are produced by various organisms living in aquatic environments, there are few reports of their effects on aquatic organisms. The effects of geosmin and MIB on sea urchin development were examined. The estimated IC₅₀ (50% inhibitory concentration) values for the formation of the fertilization membrane were 16.67 mg geosmin l⁻¹ and 68.77 mg MIB l⁻¹; those for the cell cleavage were 16.58 mg geosmin l⁻¹ and 66.86 mg MIB l⁻¹, suggesting that the toxicity of geosmin and MIB toward sea urchins are comparable to their toxicity toward Salmonella tester strains in the Ames test. These values are far greater than concentrations of these substances observed in aquatic environments with severe muddy off-flavor problems.     

Performance evaluation of canine-associated Bacteroidales assays in a multi-laboratory comparison study

The contribution of fecal pollution from dogs in urbanized areas can be significant and is an often underestimated problem. Microbial source tracking methods (MST) utilizing quantitative PCR of dog-associated gene sequences encoding 16S rRNA of Bacteroidales are a useful tool to estimate these contributions. However, data about the performance of available assays are scarce. The results of a multi-laboratory study testing two assays for the determination of dog-associated Bacteroidales (DogBact and BacCan-UCD) on 64 single and mixed fecal source samples created from pooled fecal samples collected in California are presented here. Standardization of qPCR data treatment lowered inter-laboratory variability of sensitivity and specificity results. Both assays exhibited 100% sensitivity. Normalization methods are presented that eliminated random and confirmed non-target responses. The combination of standardized qPCR data treatment, use of normalization via a non-target specific Bacteroidales assay (GenBac3), and application of threshold criteria improved the calculated specificity significantly for both assays. Such measures would reasonably improve MST data interpretation not only for canine-associated assays, but for all qPCR assays used in identifying and monitoring fecal pollution in the environment.     

Earthy odor compounds production and loss in three cyanobacterial cultures

Geosmin and 2-methylisoborneol (MIB) related odor events caused by cyanobacteria have been a very common problem to water supply. This paper investigated the effects of temperature (18 and 25 °C) and light intensity (10 and 100 μmol photons m⁻² s⁻¹) on the production behaviors of earthy odor compounds by three odorous cyanobacteria, i.e., the geosmin-producing planktonic Anabaena circinalis (Ana 318), geosmin-producing benthic Phormidium amoenum (Pho 012) and MIB-producing benthic Phormidium sp. (Pho 689). At the same time, the effects of biodegradation and volatilization on the fates of the released odor compounds in water were also evaluated. The combination of high temperature (25 °C) and light intensity (100 μmol photons m⁻² s⁻¹) favored the growth of the three cyanobacteria and the production of chl-a and odor compounds. However, higher chl-a and odor yields (average odor compounds per cell) were achieved for the two benthic cyanobacteria at the temperature of 18 °C. Most of geosmin was included within the cells for Ana 318 (95-99%) and Pho 012 (85-60%), while only 20-40% MIB was bound to the cells for Pho 689. The half-life times of MIB and geosmin due to volatilization varied between 18.8 and 35.4 days, while 8 out of 10 samples exhibited a half-life time (t_1/2) for geosmin biodegradation shorter than 1 day (0.38-15.0 h), showing that biodegradation could affect the fate of geosmin significantly in aquatic environments. In comparison, biodegradation of MIB was much slower (t_1/2: 122-2166 h). Denaturing gradient gel electrophoresis (DGGE) analysis showed that Pseudomonas- and Sphingomonas-like bacteria coexisted with cyanobacteria in the cultures, and may have played an important role in geosmin/MIB biodegradation. The result of this study will be helpful for better understanding and managing the earthy odor problems caused by cyanobacteria in water supply.     

Ultrasonically induced degradation of 2-methylisoborneol and geosmin

2-Methylisoborneol (MIB) and geosmin (GSM) are taste and odor compounds produced by cyanobacteria in surface waters. While the strong odors and musty flavors of MIB and GSM are generally associated with poor water quality, the removal of these semi-volatile compounds presents a significant challenge to drinking water providers. Likewise in aquaculture, accumulation of these compounds in fish meat leads to quality problems and reduces marketability. Conventional water treatments are ineffective at removing low concentration of odor compounds. We report herein ultrasonic irradiation at 640 kHz leads to rapid degradation of MIB and GSM. While radical processes generally dominate during ultrasonic-induced degradation, pyrolysis appears to be responsible for a significant fraction of the observed degradation. Several pyrolytic products from MIB and GSM have been identified and degradation pathways are elucidated. The degradation of MIB and GSM follows the first-order kinetics and the rate constants are 0.07 and 0.12 min(-1), respectively. These results suggest ultrasonic irradiation maybe applicable as an effective method for removal of taint compounds from potable water supplies and fish farms.     

The management of undesirable cyanobacteria blooms in channel catfish ponds using a constructed wetland: Contribution to the control of off-flavor occurrences

An exploratory study on the management of undesirable cyanobacteria blooms with respect to off-flavor problems using an integrated vertical-flow constructed wetland (CW) was performed at a small commercial-scale channel catfish farm from 2004 to 2007. The results of the three-year experiment indicated that water treatment by the CW could reduce the possibility of dominance by undesirable cyanobacteria species that often cause off-flavor problems. A detailed investigation in 2007, showed that the concentrations of geosmin, MIB (2-methylisoborneol), and β-cyclocitral in the water of the recirculating pond (4.3 ng L⁻¹, U.D. (undetected) and 0.2 ng L⁻¹, respectively) treated by the CW were significantly lower than those in the control pond (152.6 ng L⁻¹, 63.3 ng L⁻¹ and 254.8 ng L⁻¹, respectively). In addition, the relationships among the cyanobacteria species, the off-flavor compounds and ten environmental variables were explored by canonical correspondence analysis (CCA). The results showed that Oscillatoria sp., Oscillatoria kawamurae and Microcystis aeruginosa were the main sources of off-flavor compounds in the catfish ponds. The successful manipulation of undesirable cyanobacteria species potentially resulted in lower concentrations of odorous compounds in the water of the recirculating pond. An investigation of the concentrations of geosmin and MIB in catfish fillets showed that the levels of odorous compounds were below the OTC (odor threshold concentration) values in the recirculating pond but were above the OTC values from July to October in the control pond. Water recycling by the CW could potentially be one of the best management practices to control off-flavor occurrences in aquaculture.     

New standards for the determination of geosmin and methylisoborneol in water by gas chromatography/mass spectrometry

Deuterium labelled geosmin and methylisoborneol (MIB) have been synthesized and evaluated as internal standards in the determination of geosmin and MIB in water by closed loop stripping followed by gas chromatography/mass spectrometry (GC/MS). The labelled standards were compared with chloroalkanes added as internal standards either at the time of sampling or immediately before closed loop stripping. When added at sampling time, the new standards enabled accurate determination of the geosmin and MIB present initially, even when the samples were analysed as much as 3 weeks later. The new standards gave better precision and accuracy than the chloroalkanes and overcame the underestimation of initial analyte concentration which usually results from losses of analyte through adsorption, volatilisation, biodegradation etc. during sample storage. Geosmin had a limit of detection of<0.1ng/l and 1 ng/lwas determined with a coefficient of variation (CV) of 1.2% (n = 5). MIB was determined at 1 ng/l with a CV of 3.5% (n = 5).     

Quantitative real-time PCR analysis of total and propidium monoazide-resistant fecal indicator bacteria in wastewater

A real-time quantitative PCR (qPCR) method and a modification of this method incorporating pretreatment of samples with propidium monoazide (PMA) were evaluated for respective analyses of total and presumptively viable Enterococcus and Bacteroidales fecal indicator bacteria. These methods were used in the analyses of wastewater samples to investigate their feasibility as alternatives to current fecal indicator bacteria culture methods for predicting the efficiency of viral pathogen removal by standard treatment processes. PMA treatment was effective in preventing qPCR detection of target sequences from non-viable cells. Concentrates of small volume, secondary-treated wastewater samples, collected from a publicly owned treatment works (POTW) under normal operating conditions, had little influence on this effectiveness. Higher levels of total suspended solids, such as those associated with normal primary treatment and all treatment stages during storm flow events, appeared to interfere with PMA effectiveness under the sample preparation conditions employed. During normal operating conditions at three different POTWs, greater reductions were observed in PMA-qPCR detectable target sequences of both Enterococcus and Bacteroidales than in total qPCR detectable sequences. These reductions were not as great as those observed for cultivable fecal indicator bacteria in response to wastewater disinfection. Reductions of PMA-qPCR as well as total qPCR detectable target sequences from enterococci and, to a lesser extent, Bacteroidales correlated well with reductions in infectious viruses during both normal and storm flow operating conditions and therefore may have predictive value in determining the efficiency at which these pathogens are removed.     

Evaluation of geosmin and 2-methylisoborneol on the histidine dependence of TA98 and TA100 Salmonella typhimurium tester strains

Low (ca 0.01 ppb) concentrations of the naturally occurring terpene derivatives geosmin (1α, 10β-dimethyl-9α-decalol) and 2-methylisoborneol [(1-R-exo)-1,2,7,7-tetramethyl-bicyclo-(2,2,1)-heptan-2-ol] (MIB), impart earthy/muddy “off-flavors” to many water and food resources. The presence of these “off-flavors” often elicits public concern over the safety of the affected resources. The “Ames test”, assesses the induction of reverse mutation at the histidine locus in specially constructed Salmonella typhimurium tester strains, and is a widely used index of mutagenicity. This investigation indicated that neither MIB nor geosmin, when tested up to cytotoxic levels in both the presence and absence of exogenous metabolic activation, induced a mutagenic response in either strain TA98 or TA 100 compared to controls. Doses of MIB and geosmin above 45.2 and 18.1 ppm, respectively, inhibited tester strain growth, indicating that high concentrations of these metabolites may exhibit an antimicrobial activity, possibly by a mechanism similar to that reported for certain other terpene derived alcohols. Food or water resources containing similar concentrations of geosmin or MIB would be extremely unpalatable and would probably not be consumed.     

Evaluation of low-copy genetic targets for waterborne bacterial pathogen detection via qPCR

Recent developments in water quality research have highlighted difficulties in accurately predicting the incidence of pathogens within freshwater based on the viability, culturability and metabolic activity of indicator organisms. QPCR-driven assays are candidates to replace standard culture-based methods, however, protocols suitable for routine use have yet to be sufficiently validated. The objective of this study was to evaluate five oligonucleotide primers sets (ETIR, SINV, exoT, VS1 and ipaH2) for their potential applicability in qPCR assays to detect contamination from five waterborne bacterial pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, Campylobacter jejuni, Pseudomonas aeruginosa, and Shigella flexneri). An enrichment-free qPCR protocol was also tested using S. Typhimurium-seeded source water, combining membrane filtration and mechanical, chemical and enzymatic lysis techniques to recover the bacterial cells. All five primer sets were found to have high specificity and sensitivity for the tested organisms. Four of the primers were able to detect pathogen loads as low as 10 cells/mL while 200 cells/mL of C. jejuni were detectable in pure culture. Although sensitivity decreased in an artificially contaminated environmental matrix, it was still possible to detect as few as 10 S. Typhimurium cells without enrichment. The primers and protocols evaluated in this study have demonstrated potential for further validation for possible application alongside traditional indicator techniques.     

Occurrence of dissolved and particle-bound taste and odor compounds in Swiss lake waters

The occurrence of algal taste and odor (T&O) compounds was investigated in three Swiss lakes which exhibit different nutrient levels from eutrophic to oligotrophic (Lake Greifensee, Lake Zurich and Lake Lucerne). Apart from dissolved T&O compounds, the study also encompassed particle-bound compounds, i.e., compounds that can be released from damaged algal cells during drinking water treatment. A combined instrumental (SPME-GC-MS) and sensory method was applied that allowed to detect and quantify T&O compounds in natural waters in the sub ppt to low ppt-range.In addition to the prominent T&O compounds geosmin and 2-methyl-isoborneol (MIB), four other T&O compounds could be detected in the lake waters, though all at relatively low concentrations (maximum concentrations of geosmin 19 ng L⁻¹, MIB 3 ng L⁻¹, β-ionone 27 ng L⁻¹, β-cyclocitral 7 ng L⁻¹, 2-isobutyl-3-methoxypyrazine 2 ng L⁻¹, 2-isopropyl-3-methoxypyrazine 16 ng L⁻¹). The concentration peaks typically occurred in the epilimnion during summer concurrent with a high phytoplankton biomass. Consistently, the concentration levels for most of the compounds varied substantially between the three lakes and generally decreased in the order eutrophic Lake Greifensee > mesotrophic Lake Zurich > oligotrophic Lake Lucerne. Furthermore, our data revealed that the occurrence of β-ionone was largely influenced by Planktothrix rubescens. This is the first time that a correlation between β-ionone and this cyanobacterium has been reported for natural waters.     

Cyanobacteria and earthy/musty compounds found in commercial catfish (Ictalurus punctatus) ponds in the Mississippi Delta and Mississippi--Alabama Blackland Prairie

The compounds responsible for earthy and musty "off-flavors" in farm-raised channel catfish (Ictalurus punctatus) in the southeastern United States of America are geosmin and 2-methylisoborneol (MIB), respectively. These compounds are produced by certain species of cyanobacteria (blue-green algae) that grow in the aquaculture ponds. Previous research has focused on the species of cyanobacteria found in catfish ponds in west Mississippi (the leading region of catfish production in the USA), while the species responsible for earthy/musty off-flavors in catfish produced in the Mississippi-Alabama Blackland Prairie (MABP) region (second greatest region of catfish production) have not been described. We examined water samples from commercial catfish ponds in both regions to contrast the different types of cyanobacteria and assess the prevalence of geosmin and MIB. Results established that filamentous cyanobacteria are more common in west Mississippi compared to the MABP region. Also, the MIB-producing cyanobacterium Oscillatoria perornata is present in catfish ponds in both geographic locations, and geosmin is more prevalent in catfish ponds in the MABP region than in west Mississippi.     

Removal of geosmin and methylisoborneol from drinking water by adsorption on ultrastable zeolite-Y

Geosmin and 2-methylisoborneol (MIB) were removed from solutions in freshwater (100–180 ng/l) by adsorption on US-Y zeolite (SiO₂/Al₂O₃ = 80). The zeolite can be re-used by burning off the adsorbed organics. Adsorption efficiency for geosmin and MIB was not reduced by water hardness or the presence of low concentrations (5 mg C/l) of humic acid.     

Contribution of Streptomyces in sediment to earthy odor in the overlying water in Xionghe Reservoir, China

Musty and earthy odors frequently characterize the source water and fish of the Xionghe Reservoir in China. Although odorous compounds and odor-producing cyanobacteria have been analyzed in surface water, potential odorants in sediments and their contribution to the water body have remained uninvestigated. In this study, we examined the odorous compounds and possible odor-producers in the sediments and overlying water of Xionghe Reservoir from November 2007 to October 2008. High concentrations of geosmin (up to 5280.1 ng kg⁻¹ dw⁻¹) were detected in sediments, and eight strains of Streptomyces isolated from sediments were verified as producers of geosmin and/or 2-MIB in M liquid medium by HSPME-GC-MS. Geosmin concentrations in the overlying water were correlated with those in the sediments (r = 0.838, p < 0.05). In vitro studies showed that geosmin in the overlying water was released from the sediment, and that within 12 days the amount released from the sediment was 21.4–51.4%. Concentrations of geosmin in sediments were positively correlated with organic matter (r = 0.642, p < 0.01), total nitrogen (r = 0.606, p < 0.01) and Chl a (r = 0.674, p < 0.01), and were negatively associated with temperature (r = −0.425, p < 0.05). This study indicates that odorous compounds that are released from sediments should be taken into account when assessing the sources of these odorants in waters.     

Rapid decay of host-specific fecal Bacteroidales cells in seawater as measured by quantitative PCR with propidium monoazide

We investigated the persistence of feces-derived Bacteroidales cells and their DNA in seawater under natural conditions using an optimized chemical method based on co-extraction of nucleic acids with propidium monoazide (PMA), which interferes with PCR amplification of molecular markers from extracellular DNA and dead bacterial cells. The previously validated Bacteroidales assays BacUni-UCD, BacHum-UCD, BacCow-UCD, and BacCan-UCD were utilized to determine concentrations of Bacteroidales genetic markers targeting all warm-blooded animals, humans, cows and dogs, specifically, over a period of 24 d. Microcosms containing mixed feces in dialysis tubing were exposed to seawater under flow-through conditions at ambient temperature in the presence and absence of sunlight. Using a two-stage plus linear decay model, the average T₉₉ (two-log reduction) of host-specific Bacteroidales cells was 28 h, whereas that of host-specific Bacteroidales DNA was 177 h. Natural sunlight did not affect the survival of uncultivable Bacteroidales cells and their DNA with the exception of the BacCow-UCD marker. Bacteroidales DNA, as measured by quantitative PCR (qPCR) without PMA, persisted for as long as 24 d at concentrations close to the limit of detection. Culturable Enterococcus cells were detected for only 70 h, whereas Enterococcus cells measured by qPCR with and without PMA persisted for 450 h. In conclusion, measuring Bacteroidales DNA without differentiating between intact and dead cells or extracellular DNA may misinform about the extent of recent fecal pollution events, particularly in the case of multiple sources of contamination with variable temporal and spatial scales due to the relatively long persistence of DNA in the environment. In contrast, applying qPCR with and without PMA can provide data on the fate and transport of fecal Bacteroidales in water, and help implement management practices to protect recreational water quality.     

Removal of MIB and geosmin using granular activated carbon with and without MIEX pre-treatment

This study assessed the impact of MIEX pre-treatment, followed by either coagulation or microfiltration (MF), on the effectiveness of pilot granular activated carbon (GAC) filters for the removal of the taste and odour compounds, 2-methylisoborneol (MIB) and geosmin, from a surface drinking water source over a 2-year period. Complete removal of MIB and geosmin was achieved by all GAC filters for the first 10 months, suggesting that the available adsorption capacity was sufficient to compensate for differences in dissolved organic carbon (DOC) entering the GAC filters.Reduction of empty bed contact time (EBCT), in all but one GAC filter, resulted in breakthrough of spiked MIB and geosmin, with initial results inconclusive regarding the impact of MIEX pre-treatment. MIB and geosmin removal increased over the ensuing 12 months until complete removal of both MIB and geosmin was again achieved in all but one GAC filter, which had been pre-chlorinated. Autoclaving and washing the GAC filters had minimal impact on geosmin removal but reduced MIB removal by 30% in all but the pre-chlorinated filter, confirming that biodegradation impacted MIB removal. The impact of biodegradation was greater than any impact on GAC adsorption arising from DOC differences due to MIEX pre-treatment. It is not clear whether, at a lower initial EBCT, MIEX pre-treatment may have impacted on the adsorption capacity of the virgin GAC.The GAC filter maintained at the longer EBCT, which was also pre-chlorinated, completely removed MIB and geosmin for the period of the study, suggesting that the greater adsorption capacity was compensating for any decrease in biological degradation.     

Sensitive detection of sample interference in environmental qPCR

Sample interference in environmental applications of quantitative PCR (qPCR) can prevent accurate estimations of molecular markers in the environment. We developed a spike-and-recovery approach using a mutant strain of Escherichia coli that contains a chromosomal insertion of a mutant GFP gene. The method was tested in water samples by separately reducing extraction efficiency or adding humic acids and ethanol, compounds that often contaminate environmental DNA extracts, and analyzing qPCR amplification of the spiked E. coli control and human fecal Bacteroides markers (HF183 and HF134). This approach, coupled with previously developed kinetic outlier detection (KOD) methods, allowed sensitive detection of PCR inhibition at much lower inhibitor concentrations than alternative approaches using Cq values or amplification efficiencies. Although HF183 was more sensitive to the effects of qPCR inhibitors than the E. coli control assay, KOD methods correctly identified inhibition of both control and HF183 assays in samples containing as little as 0.1 ng humic acids per reaction or 5% ethanol. Because sigmoidal modeling methods allow distinction of qPCR inhibition from poor DNA recovery, we were able to simultaneously identify qPCR-inhibited reactions and estimate recovery of nucleic acids in environmental samples using a single control assay. Since qPCR is currently used to estimate important water quality parameters that have serious economic and human health outcomes, these results are timely. While we demonstrate the methods in the context of water quality regulation, they will be useful in all areas of environmental research that use qPCR.     

Analytical comparison of nine PCR primer sets designed to detect the presence of Escherichia coli/Shigella in water samples

The analytical performance of 9 different PCR primer sets designed to detect Escherichia coli and Shigella in water has been evaluated in terms of ubiquity, specificity, and analytical detection limit. Of the 9 PCR primer sets tested, only 3 of the 5 primer sets targeting uidA gene and the primer set targeting tuf gene amplified DNA from all E. coli strains tested. However, of those 4 primer sets, only the primer set targeting the tuf gene also amplified DNA from all Shigella strains tested. For the specificity, only the primer sets targeting the uidA gene were 100% specific although the primer sets targeting 16S rRNA, phoE, and tuf genes only amplified Escherichia fergusonii as non-specific target. Finally, the primer set targeting the 16S-ITS-23S gene region, was not specific as it amplified DNA from many other Enterobacteriaceae species. In summary, only the assay targeting the tuf gene detected all E. coli/Shigella strains tested in this study. However, if it becomes important to discriminate between E. coli and E. fergusonii, assays targeting the uidA gene would represent a good choice although none of them were totally ubiquitous to detect of the presence of Shigella strains.     

Escherichia coli, enterococci, and Bacteroides thetaiotaomicron qPCR signals through wastewater and septage treatment

Fecal indicators such as Escherichia coli and enterococci are used as regulatory tools to monitor water with 24 h cultivation techniques for possible input of sewage or feces and presence of potential enteric pathogens yet their source (human or animal) cannot be determined with routine methods. This critical uncertainty has furthered water pollution science toward new molecular approaches. Members of Bacteroides genus, such as Bacteroides thetaiotaomicron are found to have features that allow their use as alternative fecal indicators and for Microbial Source Tracking (MST). The overall aim of this study was to evaluate the concentration and fate of B. thetaiotaomicron, throughout a wastewater treatment facility and septage treatment facility. A large number of samples were collected and tested for E. coli and enterococci by both cultivation and qPCR assays. B. thetaiotaomicron qPCR equivalent cells (mean: 1.8 × 10⁷/100 mL) were present in significantly higher concentrations than E. coli or enterococci in raw sewage and at the same levels in raw septage. The removal of B. thetaiotaomicron target qPCR signals was similar to E. coli and enterococci DNA during the treatment of these wastes and ranged from 3 to 5 log₁₀ for wastewater and was 7 log₁₀ for the septage. A significant correlation was found between B. thetaiotaomicron marker and each of the conventional indicators throughout the waste treatment process for both raw sewage and septage. A greater variability was found with enterococci when compared to E. coli, and CFU and equivalent cells could be contrasted by various treatment processes to examine removal and inactivation via septage and wastewater treatment. These results are compared and contrasted with other qPCR studies and other targets in wastewater samples providing a view of DNA targets in such environments.     

GAC adsorber design protocol for the removal of off-flavors

This paper investigates the effectiveness of granular activated carbon (GAC) for removing off-flavor compounds of water—geosmin and 2-methylisoborneol (MIB). More specifically, it focuses on the development of an appropriate modeling approach and experimental protocol for the design of fixed-bed GAC adsorbers. Adsorption equilibrium, rate and long-term mini-column studies were conducted on a bench-scale for geosmin and MIB to estimate the equilibrium and mass-transfer parameters required for adsorber modeling. The dispersed flow homogeneous surface diffusion model (DFHSDM) was used for the prediction/simulation of the adsorber dynamics. Scale-up procedures based on dimensional analysis and similitude were employed for the design of full-scale adsorbers from bench-scale adsorbers, and for performance forecasting of full-scale adsorbers under different operating conditions. More importantly, operation and maintenance (O & M) costs were estimated for full-scale adsorbers directed at the removal of off flavor compounds, based on carbon utilization rates and disposal costs. These estimates were obtained for different plant capacities and empty bed contact times (EBCTs).     

The application of powdered activated carbon for MIB and geosmin removal: predicting PAC doses in four raw waters

Blooms of blue-green algae in reservoirs often produce the musty-earthy taste and odour algal metabolites 2-methylisoborneol (MIB) and geosmin. MIB and geosmin are not removed by conventional water treatment and their presence in the distribution system, even at low ng L-1 levels, can result in consumer complaints. Powdered activated carbon (PAC) can effectively remove MIB and geosmin when the correct dose is applied. The homogeneous surface diffusion model (HSDM) was used to predict PAC doses required to reduce MIB and geosmin concentrations to below 10 ng L-1 at four water treatment plants in Adelaide, South Australia. In jar tests, undertaken under treatment plant conditions, the predicted doses were found to produce water of the desired quality in three of the four waters. The poor predictions found in the fourth water, which had a considerably higher turbidity, were attributed to the incorporation of PAC in a larger, denser floc, leading to a reduced effective contact time of the adsorbent. It was found that higher doses of PAC were required for both compounds to produce acceptable quality water when turbidities rose above 26 NTU.