Is Atmospheric Particulate Matter Inhibiting Marine Primary Productivity? John T. Hardy* and Eric A. Crecelius Marine Research Laboratory,+ 439 W. Sequim Bay Road, Sequim, Washington 98382
Present deposition rates of atmospheric particulate matter do not appear great enough to inhibit marine primary productivity except, perhaps, at the sea-surface microlayer. Milligramhter quant,ities of air particulate matter added to seawater result in an exponential reduction in photosynthetic 14C assimilation of natural marine phytoplankton populations. Urban particles are 6 times more toxic than rural particles. The ratios of soluble trace elements from equal amounts of urban (Seattle) to rural (Quillayute) atmospheric particles are as follows: As, 112; Br, 6.4; Cr, 3.4; Cu, 3.7; Ni, 3.0; Pb, 36; V, 2.7; and Zn, 2.2. Introduction Air particulate matter from urban areas generally contains higher levels of toxic metals ( 1 , 2 ) , especially lead from the combustion of gasoline containing tetraethyllead, than rural areas ( 3 ) .Pollution of the atmosphere by metal-rich, airborne particles now occurs on a global scale ( 4 ) . The continued combusion of fossil fuels and plans for expanded dependence upon coal and synthetic fuels raise increasing concern about the potential environmental effects of atmospheric emissions. Environmental studies in coastal areas have tended to focus on direct water discharge of urban industrial wastes, but there is growing evidence that atmospheric deposition may be responsible for relatively high proportions of the DDT, PCB, hydrocarbons, and trace metals entering aquatic environments (4-9). Once reaching the ocean, many particulate-borne metals can be leached into seawater with solubilities ranging from 30% to 80% ( 1 0 , I I ) . Despite the known toxicities of individual substances associated with air particles and their documented entrance into the marine environment, no studies, to our knowledge, have characterized the overall toxicities or bioavailabilities of typical atmospheric particulates to marine organisms. The purpose of our study was to determine the effect of airborne particulate matter on marine phytoplankton productivity. Methods and Materials Air particles were collected from one rural coastal site and two urban sites. The rural site (Quillayute, WA) is located 5 km from the Pacific Ocean and has been used by others for sampling air masses with a trans-Pacific trajectory (12).One urban site was a t the University of Washington campus in Seattle, WA. We also used urban air particles collected by the U.S. National Bureau of Standards (SRM-1648) in the St. Louis area using a baghouse type of collector (13). Because of absorbed water, the actual weight of particulate matter collected on the Whatman 41 filters could not be accurately determined. Thus, the weight of particulate matter was estimated by using the Fe content of the filters and the average Fe content of air particulate matter at the specific site as determined by Fe analyses of weighed glass-fiber filters. Monthly air particulate matter samples (each collected for a 4-6-day period) were collected for 1yr on weighed glass-fiber filters to determine total suspended particulate mass and Fe
+ Pacific Northwest Laboratory, operated by Battelle Memorial Institute.
0013-936X/81/0915-1103$01.25/0 @ 1981 American Chemical
Society
content. The metal concentrations in both the glass and paper filters were determined by X-ray fluorescence (14). Measurements of phytosynthetic carbon fixation by natural marine phytoplankton were performed by following, in general, the 14C technique (15).Sea-surface bucket water samples were collected from Sequim Bay, a relatively unpolluted extension of the Straits of Juan de Fuca ca. 72 km northwest of Seattle, WA. The seawater was passed through a 250-pm mesh net to remove the larger zooplankton and dispensed into 500-mL transparent and opaque Teflon bottles. Light intensity was measured with a Li-Cor Model 185A photometeF. The transparent bottles did not significantly reduce available light energy. In the case of St. Louis air particles, different volumes of a solution containing 10 mg/mL particulate (under constant agitation to maintain the suspension) were pipetted into the light and dark seawater bottles. In the case of the Seattle and Quillayute samples, filters containing known weights of particulates were cut into 1-cm squares, and different amounts of paper, along with their particurate load, were added to the light and dark bottles. Duplicate light bottles and one dark bottle were used for each air particulate concentration. One milliliter of sterile seawater containing 10 pCi of NaH14C03 was then added to each bottle. The bottles were incubated for 4 h (1030-1330 f 0.5 h) in an outdoor sea table a t the same temperature at which they were collected. After incubation, the seawater from each bottle was filtered at 15 psi through a 0.45-pm Millipore filter. The filter was rinsed with clean seawater and then fumed over concentrated HC1 for 1 min to remove inorganic carbon (16).The filters were added to scintillation vials, 20 mL of Aquasol was added, and the radioactivity was determined in a Beckman Model 123-350 liquid scintillation counter. A quenching curve of external standard ratio vs. counting efficiency was constructed, and all uncorrected 14Ccounts were corrected for loss of efficiency due to quenching and expressed as dpm. The solubilities of six elements collected on paper filters and SRM-1648 were determined by neutron activation of the particulates, followed by a 1-h contact with seawater before filtering through a 0.4-pm membrane filter as described by Crecelius (10).The solubilities of Cu and P b were determined by differential pulse anodic stripping voltametry ( 1 7 ) .
Results and Discussion The air particulate mass loadings at Quillayute and Seattle ranged from 7 to 33 pg/m3 (mean 16) and from 21 to 101 pg/m3 (mean 39), respectively. A composite sample of four Quillayute paper filters was selected for the 14Cuptake experiments. This composite sample represented “clean-air” periods when the average elemental air concentrations were as follows (ng/m3): Fe, 52; Cu, 0.91; Pb, 2.2; and Zn, 3.4. A composite sample of three Seattle filters had averaged elemental air concentrations of 306 (Fe), 9.6 (Cu), 180 (Pb), and 20 (Zn) ng/m3. The major differences in elemental composition of Quillayute and Seattle particles are the high C1 content of Quillayute due to sea salt and the high content of As and P b in Seattle due to urban air pollution. Compared to St. Louis particles, Seattle particles are enriched in As, Br, C1, and P b but are otherwise similar in elemental content (Table I). The elemental solubilities of these three particulate matter samples are similar and agree with those reported by Hodge Volume 15, Number 9, September 1981 1103
Table 1. Elemental Concentrations of Air Particulate Matter (pglmg) and Percent Solubility of Elements in Seawater Qulllayute
wmg
As
0.014
Br Cd
0.95 NA a
CI
Fe
K
ia
cu
50 98
410
0.0 17 0.24 13.7
Cr
w m g
% soluble
w m g
1.4
56
0.115
42
6.2 NA a
96
0.50 0.075 4.5 0.403 0.609 39.1 10 0.86 0.082 6.6 NA a 0.024 NA a 4.0 0.13 4.76
90
17 14b
0.19
9
44
0.95
41
8b 88
30 6.5
Mn
0.34
0.61
Ni
0.08
0.24
Pb Rb
0.57 0.024
54
17.9
Se
0.019
27
