Status of Metal Contamination in Surface Waters of the Coastal Ocean

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Status of Metal Contamination in Surface Waters of the Coastal Ocean off Los Angeles, California since the Implementation of the Clean Water Act Emily A. Smail,*,† Eric A. Webb,† Robert P. Franks,‡ Kenneth W. Bruland,‡ and Sergio A. Sañudo-Wilhelmy† †

Department of Biological Sciences and Department of Earth Sciences, University of Southern California, Marine Biology and Biological Oceanography, Los Angeles, California 90089-0371, United States ‡ Department of Ocean Sciences, University of California at Santa Cruz, Santa Cruz, California 95064, United States S Supporting Information *

ABSTRACT: In order to establish the status of metal contamination in surface waters in the coastal ocean off Los Angeles, California, we determined their dissolved and particulate pools and compared them with levels reported in the 1970s prior the implementation of the Clean Water Act. These measurements revealed a significant reduction in particulate toxic metal concentrations in the last 33 years with decreases of ∼100-fold for Pb and ∼400-fold for Cu and Cd. Despite these reductions, the source of particulate metals appears to be primarily anthropogenic as enrichment factors were orders of magnitude above what is considered background crustal levels. Overall, dissolved trace metal concentrations in the Los Angeles coastal waters were remarkably low with values in the same range as those measured in a pristine coastal environment off Mexico’s Baja California peninsula. In order to estimate the impact of metal contamination on regional phytoplankton, the internalization rate of trace metals in a locally isolated phytoplankton model organism (Synechococcus sp. CC9311) was also determined showing a rapid internalization (in the order of a few hours) for many trace metals (e.g., Ag, Cd, Cu, Pb) suggesting that those metals could potentially be incorporated into the local food webs.

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INTRODUCTION The Southern California Bight (SCB) is a densely populated and industrialized area subject to high levels of anthropogenic inputs from wastewater treatment plants, urban and agricultural runoff, oil and gas production, vessel activities, and hazardous material spills.1 Nowhere is this more evident than in the coastal ocean off Los Angeles, California. Los Angeles County houses an estimated 10 million inhabitants2 that, together with other SCB counties, generate more than 4.7 billion gallons of treated effluent water per day.3 This effluent water is discharged into the coastal ocean by nineteen municipal wastewater treatment plants serving the Los Angeles area, including the large Hyperion Treatment Plant (HTP) (City of Los Angeles) and the Joint Water Pollution Plant (JWPCP) (Los Angeles County Sanitation Districts).3 This effluent water is discharged five miles offshore at a depth of 60 m.4 While regulation through the Clean Water Act led to a large reduction in the input of pollutants into the SCB beginning with its implementation in 1972,5 effluent discharge from those wastewater treatment plants continues to discharge several metric tons of toxic metals such as Ag, Cu, Ni, Pb, and Zn into the Bight every year.3,6,7 © 2012 American Chemical Society

Current monitoring programs within the SCB have primarily focused on determining temporal and spatial changes in metal contamination in sediments and biota,8−11 and, therefore, current data on the concentrations of water-column particulate and dissolved metals in the marine environment off Los Angeles are very limited. There is also no information about metal accumulation within local phytoplankton species even though several studies have shown that environmentally relevant trace metals, including Cu, Ni, Pb, and Cd are readily internalized by phytoplankton.12−16 In this study, we assayed the impact of the Clean Water act on toxic trace metals in surface waters of the SCB off Los Angeles by determining current levels of particulate and dissolved metals and comparing these levels to measurements done in the same locations in the early 1970s by Bruland and Franks (1978).17 In addition, enrichment factors calculated for particulate trace metals and a comparison of dissolved trace metal levels measured off Los Angeles with those measured in a Received: Revised: Accepted: Published: 4304

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determine which particulate metals are likely to be readily desorbed from suspended particles (labile) from those more strongly bound (refractory).17 The labile pool was determined by placing the filters in an acetic acid leach (20% Optima grade acetic acid for two hours). After the labile leach, the refractory metal pool was then obtained by boiling the filters for 45 min in acid-washed Teflon digestion bombs with Optima grade HF, HCl, and HNO3. Total particulate trace metal concentrations are reported as the labile + refractory trace metal pools. Trace metal levels in all the particulate and dissolved pools were quantified by ICPMS using external calibration curves and an internal indium standard. Phytoplankton Metal Internalization Experiments. Axenic cultures of a Synechococcus sp. CC9311, a strain isolated from the California current, were grown in filtered, amended SCB seawater (collected using trace metal clean techniques from the San Pedro Oceanographic Times Series station (SPOTS) during November 2009) in acid washed polycarbonate containers at 18 °C at a 12/12 light cycle of 100 μmol photons m−2 s−1. The SCB media was microwave sterilized,22 pH adjusted to 8.0−8.2 with sodium hydroxide, and amended with N and P (final concentrations: 8.0 × 10−4 M Optima grade nitric acid and 5.0 × 10−5 M phosphoric acid). Cultures were acclimated to the modified SCB seawater media for 3 transfers prior to transfer to 2 L experimental vessels. The purity of the cultures was confirmed at each time point via examination of DAPI (4′,6-diamidino-2-phenylindole) stained aliquots using a Zeiss Axiostar epifluorescent microscope and subsample addition to Marine Purity Broth.23 Cell growth was estimated through microscopic examination and flow cytometry at each time sampling point. For flow cytometry (FC), samples were fixed with a final concentration of 0.1% formalin prior to analysis and run along with an internal standard of BD on a FACSCalibur Flow Cytometer. FC results were analyzed using the CellQuest software (BD Biosciences). Trace metals internalization experiments were performed in 2 L acid washed polycarbonate bottles that were amended with bioactive (nutrient and toxic) trace metals at concentrations approximately 5× the dissolved concentrations found at neareffluent discharge stations in the Palos Verdes area during February 2009 (0.5 nM Al, 15 nM Ni, 10 nM Cu, 0.05 nM Ag, 1 nM Cd, 0.3 nM Pb, 595 nM Mo, 1 nM Co, 15 nM Zn, and 15 nM Fe). Amended and control cultures were filtered down at 0, 3, 6, 12, 24, and 48 h after trace metal additions. At each time point, 50 mL aliquots were filtered onto acid-washed 0.45 μm polycarbonate filters for total metal and intracellular metal concentrations. The intracellular pool was determined using the oxalate wash procedure.24,25 Trace metals were extracted with heated acid digestions in sealed Teflon vessels containing Optima grade nitric and hydrochloric acids. Trace metal analysis of digested solutions was performed by ICPMS as described above. Trace metal detection limits and procedural blanks can be found in the Supporting Information.

pristine environment off Punta Banda, Baja California, Mexico (33° N, 117° W) and elsewhere in the SCB in 1989 were used to evaluate the current status of metal contamination within this area of the Bight. In order to more fully understand the ecological impact of dissolved metals in these coastal waters, we also determined trace metal internalization in the cyanobacteria Synechococcus sp. CC9311 in an attempt to establish the potential for biological uptake by local phytoplankton.

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MATERIALS AND METHODS Sample Collection and Study Site. Surface water samples were collected in the SCB off Los Angeles in February and September of 2009 (Figure 1). February samples were collected

Figure 1. Map of SCB sampling sites with potential sources of metal input indicated with arrows. Sampling locations are identified using the station numbers of the Los Angeles County Sanitation District and the City of Los Angeles Sanitation District monitoring programs. Map was generated using Ocean Data View.18

in collaboration with the Los Angeles County Sanitation District and the City of Los Angeles Sanitation District, and September samples were collected in collaboration with the USC Wrigley Institute for Environmental Studies. Station numbers correspond to environmental monitoring stations of these agencies. Detailed descriptions of the physical setting of the sampling area have been previously reported.19,20 All samples were collected using trace metal clean techniques at a depth of approximately 1−2 m from the surface and refrigerated until filtration (0.45 μm) and dissolved ( Ba > Zn > V > Ni > Cu > Fe > Co (Figure 3B). The most highly enriched particulate metals were Pb and Cd, which had ratios of, on average, ∼4 and ∼2 orders of magnitude above crustal levels, respectively. Both Cd and Pb have shown elevated enrichment factors relative to other metals and have been therefore implicated as having anthropogenic sources.38,40 Cu, another particulate trace metal of interest due to its known toxicity to picoplankton and association with antifouling paint,6,34,41 had enrichment factors ∼1−2 orders of magnitude above crustal levels in stations near the Port of Long Beach and the San Gabriel and Los Angeles rivers. The elevated enrichment factor of Ba also suggests an anthropogenic source of this particulate metal, while the lower EFs for the remaining metals indicates that these metals are likely to have primarily natural sources. Further research will be required to definitively link the distribution of these metals to specific sources and calculate realistic mass balance estimates for the SCB. Distribution of Dissolved Trace Metals. Variations in water circulation patterns within the SCB and stormwater runoff and sewage are likely to be major factors affecting the distribution of dissolved trace metals in the Los Angeles area. The major point sources influencing metal levels in the February 2009 cruise appear to be the San Gabriel River as elevated levels of Ag (13 pM), Cu (5 nM), Cd (210 pM), and Pb (100 pM) were all detected near the river outflow (Figure 4). Mean and median concentrations for dissolved metals for that cruise (mean ± standard deviation/median) were Ag, 6.8 ± 3.6 pM/6.3 pM; Cu, 1.4 ± 0.9 nM/1.1 nM; Cd, 120 ± 31 pM/118 pM; and Pb, 43 ± 18 pM/37 pM. To a lesser extent, relatively high levels (∼12 pM) of sewage-tracer Ag29 were also measured in the vicinity of the JWPCP and HTP effluent discharge outfalls (Figure 4). The elevated levels of Ag in these areas (San Gabriel River outflow and near JWPCP and HTP’s outfalls) suggest that some effluent discharge reached the surface waters of these locations. In contrast to the geographic patterns observed in February, relatively high dissolved metal concentrations in September were observed at stations located north of the Palos Verdes Peninsula (4 nM Ni; 49 nM V; 169 nM Mo; 172 pM Co; 7 pM Ag,) and off of Point Dume (252 pM Cd; 12 nM Fe) (Figure 5 and Figure S4 in the Supporting Information). The mean and median dissolved concentrations of these metals in September 2009 (mean ± standard deviation/median) were Ni, 2.0 ± 0.5 nM/2.0 nM; V, 20 ± 6.8 nM/19 nM; Mo, 67 ± 22 nM/64 nM; Co, 66 ± 34 pM/55 pM; and Ag, 2.9 ± 1.3 pM/2.6 pM. Coastal currents and upwelling events could potentially explain the seasonal variations observed for some metals such as Cd, Co, Ni, Mo, V, and Fe that are strongly influenced by circulation patterns, seasonal nutrient distributions, and biological activity.46−50 As the February sampling was carried out during the rainy season (2.15−3.65 in. of precipitation measured at Santa Monica and Palos Verdes during the week of our cruise),42 differences in metal concentrations and distributions are also likely to be related to variations in river inputs (mean discharge from the San Gabriel River of 0.067 ft3/ s in February 2009 vs 0.0 ft3/s in September 2009)43 and stormwater runoff, which are potentially large source of heavy metals to the SCB.1,44,45

Figure 3. (A) Particulate metal concentrations measured at the neareffluent outflow stations in February 1976 (black bars) and February 2009 (gray bars). The1976 values are mean values obtained at stations 443 (surface sample) and 361 (10 m off the bottom).17 The 2009 concentrations are mean ± standard deviation from stations 2802, 2903, and 3504 (Figure 1). The location of the 2009 stations was selected based on their proximity to 1976 stations. Station coordinates are available in the Supporting Information. (B) Box-plots of the enrichment factors (EF) for particulate metals calculated for all February 2009 stations. The dashed line represents the EF 1 order of magnitude above what is considered crustal levels.35,36

The overall characteristics of the particulate trace metals in surface water samples remained largely unchanged with the average percent labile particulate metals being lower in 1976 but within the same range (97% labile Cd in 1976 vs 91% ± 20 labile Cd in 2009; 38% labile Cu in 1976 vs 52% ± 30 labile Cu in 2009; 61% labile Pb in 1976 vs 76% ± 26 labile Pb in 2009; 62% labile Zn in 1976 vs 54% ± 29 labile Zn in 2009; 64% labile Ba in 1976 vs 42% ± 27 labile Ba in 2009; 67% labile V in 1976 vs 45% ± 27 labile V in 2009) with the exception of Ni which had a lower average percentage of labile particulates in 2009 (57% labile Ni in 1976 vs 27% ± 25 labile Ni in 2009). The reduction in particulate metal levels observed in the last 33 years in the coastal ocean off Los Angeles is not due to improvements in sample collections and/or analytical protocols as both sets of samples were collected and analyzed using similar protocols. Furthermore, to reduce the seasonal and spatial variability, both sampling campaigns took place in February (1976 and 2009) at the same locations or within the vicinity of each other. Potential Sources of Particulate Trace Metals. The source of particulate Cu, Ni, Zn, Ba, Cd, Pb, and Ba appears to be primarily from anthropogenic sources. This is based on an enrichment factor analysis (EF) in which metal concentrations are normalized using the equation [Metal]/[Fe]sample/[Metal]/ [Fe]crust where [Metal]/[Fe]sample represent the concentration of the metal of interest and Fe in the particulate surface water sample and [Metal]/[Fe]crust represent the average concen4307

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Figure 4. Concentration gradient maps of dissolved Ag, Cu, and Cd measured in February and September 2009 in the SCB. The metal concentration range is indicated with the different colors. Maps were generated using Ocean Data View.18

suspended particulates may be a source of dissolved Cu and Pb. This trend was not seen for other trace metals including Cd, which had virtually no association between labile and dissolved pools despite nearly 100% of Cd particulates being labile in nature (Table S2 Supporting Information). The sources of these particulate trace metals in the SCB have primarily been associated with antifouling paint for Cu and stormwater runoff and remobilization from sediments contaminated with Pb before the elimination of unleaded gasoline. Deposition of Cu and Pb into the SCB has resulted in enrichment of these metals in approximately 20% of the SCB area with metals loads being especially high in some coastal regions such as the Palos Verdes Shelf, harbors, and industrialized port areas.8

In addition to point sources, desorption from suspended particles also appears to be an important process influencing the concentration of some dissolved metals in the coastal ocean off Los Angeles. This is evidenced by significant correlations between the dissolved and the labile particulate pool for Cu and Pb (Figure S3 Supporting Information). Pb had the highest overall association between dissolved and labile pools (r2 = 0.61, all stations) with stations having high particulate Pb values showing a stronger association (r2 = 0.92, stations with particulates ≥4.6 nM Pb) (Figure S3B Supporting Information). Cu also showed an association with 17 out of 29 stations occurring within a 95% confidence interval of a linear regression (r2= 0.37; Figure S3A Supporting Information). These associations indicate that surface desorption from 4308

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Figure 5. Box-plots of dissolved Cu, Ag, Pb, and Cu concentrations measured in the SCB in 1989 and in 2009 and in Punta Banda, Mexico. SCB 1989 concentrations were measured at near shore stations from Point Loma, Coronado, Imperial Beach, and the US-Mexico Border.29,47,51,52 SCB 2009 values are all the metal concentrations measured in February and September 2009 in our area of study. Punta Banda concentrations include all the measurements in samples collected every 2 weeks from March 2004−April 2005 (Supporting Information). The arrows identify specific locations or oceanographic processes where or when the metal concentrations were significantly higher.

Temporal Gradients in Dissolved Trace Metals in the SCB Surface Waters. A comparison of dissolved metal concentrations measured in this study with those measured in 1989 in the SCB29,47,51,52 suggests that median metals levels in surface waters of the Bight have declined in general by a factor of 2 for Ni, Cu, and Cd and by a factor of 3 for Ag, Co, and Pb (Figure 5). Specifically, compared to the concentrations of trace metals measured in the SCB 20 years ago, average values are slightly lower for Cd, Cu, Ni, Ag, and Pb in 2009 (158 ± 15 pM Cd in 1989 vs 134 ± 36 nM in 2009; 2.4 ± 0.4 nM Cu in 1989 vs 1.3 ± 0.7 in 2009; 16 ± pM Ag in 1989 vs 5 ± 3 pM in 2009). The range of dissolved metal concentrations measured in 2009 off Los Angeles (1.2 pM − 13 pM Ag; 0.6 nM − 5 nM Cu; 93 pM − 252 pM Cd; 1.2 nM − 4.3 nM Ni) were comparable and not significantly different than the concentrations measure in the unpopulated area in Punta Banda, Mexico, used as a “control” uncontaminated region (Figure 4). In fact, dissolved Cd and Fe were slightly higher on average in Punta Banda (Cd 134 ± 36 nM in Los Angeles and 489 ± 118 nM in Punta Banda; Fe 1.2 ± 2.3 nM in Los Angeles and 4.1 ± 2.1 nM in Punta Banda). The higher levels of these metals in the Punta Banda area are most likely the result of strong upwelling that occurs on the shelf of the Baja California Peninsula.52,53 The Case of Lead. Our analysis of particulate and dissolved Pb concentrations in the coastal ocean off Los Angeles suggests that surface water contamination of this toxic metal has been reduced since the elimination of leaded gasoline and shows continuing decreases relative to previous measurements performed in the late 1980s. Dissolved Pb concentrations

were last measured in this region in 1989 when SañudoWilhelmy and Flegal (1994)51 reported a 3-fold decrease in Pb concentrations compared to the 1970s.54,55 February 2009 samples were within a similar range of near shore SCB samples collected in 1989 (mean 77 pM ± 45 in 1989 compared to mean 43 pM ± 18 in February 2009). In contrast, September 2009 samples were markedly lower with 19/26 stations having dissolved Pb concentrations below our detection limit of 8 pM. Pb concentrations had the largest difference between the two sampling months of all measured trace metals, potentially due to the strong association of this trace element with surface runoff, oceanic advection, and particle scavenging.51,55 While the dissolved levels of Pb have been significantly lowered, the legacy of Pb enriched particles from previous aeolian deposits and wastewater discharge can result in periodic pulses of dissolved Pb from desorption from suspended particulates (Figure 2, Figure S3 Supporting Information) introduced to the water column by stormwater runoff and sediments resuspension. The elevated Pb levels measured near the San Gabriel River outfall in the February 2009 samples support the aforementioned mechanism. Rapid Internalization of Trace Metals in Synechococcus sp. CC9311. Trace metal additions to axenic cultures of Synechococcus sp. CC9311 resulted in an increase in internal metal concentrations on average after 3 h of exposure for Cd (+16%), Co (+55%), Fe (+26%), Ni (+15%), Mo (+38%), Cu (+29%), and Pb (+45%) suggesting that many toxic metals can be introduced into the food chain within one tidal cycle (Figure 6). Internalization continued through the 6-h time point for Cd (+28%), Ag (+31%), Co (+60%), Fe (+58%), Ni (+59%), Mo (+49%), Cu (+58%), and Pb (+62%) with internalization of Pb 4309

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ACKNOWLEDGMENTS

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REFERENCES

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This study was supported by the National Sea Grant College Program, National Oceanic and Atmospheric Administration, U.S. Department of Commerce, under grant number NA07OAR417008. We thank Los Angeles County Sanitation Department (specifically Alex Steele), the City of Los Angeles Sanitation Department (specifically Curtis Cash and Bob Brantley), Lynda Cutter from USC, and the USC Wrigley Institute for Environmental Studies for their assistance with sample collection.

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Figure 6. Total (gray bars) and intracellular (black bars) Cu and Pb concentrations measured in Synechococcus sp. CC9311. Trace metal values are normalized to P to account for variations in biomass. Error bars are standard error of culture replicates.

and Co continuing for 12 h (+77% for Pb and +78% for Co). Al and Zn were not internalized during the course of the experiment. The exposure to the metal spike resulted in mortality of Synechococcus sp. after 48 h of exposure. While the culture media may have had a lower concentration of dissolved organic carbon (DOC) that could influence metal toxicity due to organic complexation, we do not expect this to bias our results as the majority of the metals used in our study are not strongly chelated by DOC (e.g., Ag, Cd, Ni, Pb). Furthermore, we used low nanomolar additions during our experiments, already lower than the micromolar concentrations usually used in this type of bioassay. The rapid internalization of these metals in Synechococcus sp. indicates that even small inputs of these metals into the marine environment can result in biological uptake that has the potential for subsequent transfer up in the food web and thus highlights the importance in controlling toxic metal contamination.

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ASSOCIATED CONTENT

* Supporting Information S

Station coordinates, an additional graph comparing 1976 vs 2009 particulates, 2009 particulate and dissolved trace metal values, Punta Banda dissolved trace metal values, detection limits, procedural blanks, station coordinates, additional trace metal distribution maps, and additional trace metal Synechococcus sp. internalization graphs. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Phone: (213) 740-5764. E-mail: [email protected]. Notes

The authors declare no competing financial interest. 4310

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dx.doi.org/10.1021/es2023913 | Environ. Sci. Technol. 2012, 46, 4304−4311