Concentration of Mercury in the Manufacture of Fish Protein Concentrate by Isopropyl Alcohol Extraction of Sheepshead and Carp Thomas A. Gasiewicz and Frank J. Dinan' Department of Chemistry, Canisius College, Buffalo, N.Y. 14208
rn Levels of mercury in bottom feeding freshwater fish and their corresponding fish protein concentrates have been determined and found to correlate with a fish:fish protein concentrate enrichment factor of approximately 5 . This finding indicates that no mercury is extracted from the fish used in this study during the concentrate manufacture via isopropyl alcohol extraction, and further suggests that only fish of low initial mercury concentration may be used as starting material in this process if the resultant fish protein concentrate (FPC) is not to exceed the maximum allowable mercury concentration level.
P
roduction of FPC from scavenger fish affords a route by which these fish can be converted to a form of protein which can be used as a dietary supplement (Sidwell et al., 1970). This process is of potentially great importance in the Great Lakes. In recent years, whereas the game fish population of these lakes has gradually depleted, there has been a noted increase in the population of bottom feeding or scavenger fish which have a significantly lower demand for dissolved oxygen (DO) (Beeton, 1971). These fish generally have much higher oil and amine contents than game fish and are therefore little used for human consumption. However, bottom feeding fish offer a potentially large source of material for conversion to FPC, which is a nearly tasteless and odorless material. It is well-known that the lower Great Lakes, particularly Lakes Erie and Ontario, have been extensively polluted by industrial and municipal wastes (Beeton, 1971). Since fish from these lakes would be susceptible to the ingestion and concentration of such heavy metals as mercury, this study has attempted to correlate quantitatively the level of mercury concentration in individual scavenger fish with the concentration of mercury in the FPC made from these fish. To whom correspondence should be addressed.
Two types of bottom feeding fish commonly found in the Great Lakes, sheepshead (Archosargus probatocephalus) and carp (Cyprinus carpio) were used in this study. These fish were caught in the eastern end of Lake Erie and the mouth of the Niagara River, and immediately frozen. (One sample used in this study was obtained from a stream in Hershey, Pa.) Each individual fish was finely ground without evisceration, and a representative sample taken for mercury determination. The remaining ground fish was subsequently converted to FPC using isopropyl alcohol as the extracting solvent. The procedure followed for FPC preparation was exactly that recommended by the Bureau of Commercial Fisheries (1966). In each case, a representative sample of the resulting FPC was taken for analysis. The wt % FPC obtained from the fish was carefully determined. In this way, it was possible t o correlate the mercury concentration in a given fish with that of the FPC obtained from that fish and to obtain an accurate enrichment factor for the FPC process. Mercury determinations were carried out using flameless atomic absorption (Hatch and Ott, 1968). Both whole fish and FPC samples were digested in concentrated sulfuric acid for 2 hr prior to their determination. All analyses were conducted in duplicate. Table I shows the results obtained in this study. All of the figures in this table have been adjusted for an average value of 97 % recovery of known amounts of mercuric chloride run through the digestion-analysis procedure. The quality of the FPC prepared during this study was assessed by comparing the ash (23 %), protein (72 %), and lipid (0.23 %) content of this material with the published values obtained for the same fish species (Great Lakes Laboratory, 1970). In each case, standard methods were used for the determination of these values (Association of Official Agricultural Chemists, 1965). Inspection of the data in Table I discloses that the mercury originally present in each whole fish is not removed by the extraction process. In fact, there is an observed five- to sixfold concentration factor in going from whole fish to FPC via the isopropyl alcohol process. This figure compares favorably
Table I. Mercury Enrichment Factors for F P C Preparation
Sample Sheepshead ( A . probatocephalus) Carp (C. carpio)
Theoretical enrichrnent factorb 5.1
enrichrnent factorc
Obsd
Hg concn
Catch location Niagara River
Hg concn in whole fish,u fig Hgk
0 . 2 0 C 0.03
1.21 i 0 . 1 8
obtained 19.5
Eastern Lake Erie Eastern Lake Erie
0.15 i 0.01 0.58 i 0.01
0.79 + 0.07 3.12 0.14
*
19.5 20.9
5.1 4.9
5.2 5.4
Hershey Park, Hershey, Pa.
0.11 i 0 . 0 1
0.62 5 0.02
18.0
5.5
5.6
in F P C . ~
Pg H g i s
average of two determinations with the calculated standard deviation. lOOjwt '% FPC Determined as follows: [Hg] in F P C / [ H ~in ] whole fish
a Each value listed is the b Determined a s follows:
726 Environmental Science & Technology
Wt %
FPC
5.5
Table 11. Mercury Levels in Fish and Fish Protein Concentrate Max. safe Whole Corresponding consumption of FPC, fish [Hgl, fig/g FPC [HgLa !&/g g/day 0.10 0.5 80 40 0.20 1. o 0.30 1.5 26.7 0.40 2.0 20.0 0.50 2.5 16.0 0.60 3.0 13.3 0.70 3.5 11.4 o.
Assuming a 5 :1 enrichment factor.
with a theoretical concentration factor of approximately 5 . This factor is based on the wt FPC obtained from the fish, assuming that all of the mercury originally present remains in the concentrate. The observed enrichment factors are generally slightly higher than the theoretical factor, but within the experimental error of the method. The reason for this consistently higher factor is not clear at present. The presence of mercury at levels in the range 0.3-0.9 pg Hg/g in FPC obtained from the National Center for Fish Protein Concentrate has been previously reported by Beasley (1971) who speculated that this level of mercury results from the sum of concentration processes occurring in both the environment and in FPC manufacture. However, the level of mercury concentration in the whole fish used to prepare this FPC was not determined. Therefore, the exact extent of mercury loss or concentration during the FPC manufacturing process could not be known. The approximately fivefold enhancement of mercury concentration which has been found to occur during the FPC process suggests that a definite limitation exists on the mercury concentration in fish used as starting material for the manufacture of FPC via isopropyl alcohol extraction. Table I1 shows the theoretical relationship which exists between the mercury concentration of whole fish converted to FPC and the amount of FPC which can be safely consumed. These
figures are based on a recommended maximum daily consumption of 60 pg of Hg (Berglund and Berlin, 1969) and an estimated current consumption of approximately 20 pg Hg/day (Bowen, 1966). It is further assumed that fish protein concentrate is approximately 80 protein (Ayres, 1966). Inspection of these data discloses that only 32 grams of FPC prepared from whole fish having a mercury concentration of 0.25 pg/g, which is only one half the Food and Drug Administration (FDA) recommended maximum, and not an unreasonable figure for lower Great Lakes scavenger fish, could be safely consumed. This level drops to 16 grams of FPC for material prepared from fish at the 0.5 pg Hg/g level. It is important to note, however, that the FDA guideline for mercury concentration is 0.5 pg/g and that FPC exceeding this limit cannot be sold in this country. In view of these limitations, scavenger fish taken from polluted waterways would seem to be of limited value for conversion to FPC. Furthermore, the observed concentration effect demonstrates that the heavy metals content of any FPC must be considered carefully before this material is used for human consumption. Literature Cited Association of Official Agricultural Chemists, “Official Methods of Analysis of the AOAC,” 10th ed., Washington, D.C., 1965, pp 16, 161-2. Ayres, J., Science, 152, 738 (1966). Beasley, T. M., ENVIRON. SCI. TECHNOL., 5 , 634-5 (1971). Beeton, A. M., Bull. Buffalo SOC.Natur. Sci., 25 (2), 1-20 (1971). Berglund, F., Berlin, M., “Chemical Fallout,” pp 423-32, M. W. Miller and G. G . Berg, Eds., Charles C Thomas, Springfield, Ill., 1969. Bowen, H . J. M., “Trace Elements in Biochemistry,” pp 11617, Academic Press, London, England, 1966. Bureau of Commercial Fisheries, “Marine Protein Concentrate,” Fishery Leaflet No. 584, 1966, p 27. Great Lakes Laboratory, Special Report No. 7, State Univ. of New York at Buffalo, 1970. Hatch, W. R., Ott, W. L., Anal. Chem., 40,2085 (1968). Sidwell, V. P., Stillings, B. R., Knobl, G . M., Food Technol., 24, 876-8 (1970). Received for reciew August 23, 1971. Accepted April 17, 1972
Critical Evaluation of Rate-Controlling Processes in Manual Determination of Nitrogen Oxides in Flue Gases Geoffrey Margolis Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Mass. 021 39
John N. Driscoll’ Walden Research Corp., Cambridge, Mass. 021 39
T
he most common wet chemical method for the determination of high concentrations of nitrogen oxides in the presence of sulfur dioxide is the phenol disulfonic acid (PDS) technique. Although reliable results are obtained, a serious drawback is the exceptionally long time required for analysis. This results from the long standing time and the tedious (4-6 hr) evaporation step required by the procedure. The incentive for reducing the time required is obvious. The objective of this paper was, therefore, to evaluate critically
the entire procedure, identify any rate-controlling steps and make changes to substantially reduce the time required. Consideration of the equilibrium constants of Stull (1965) for the nitrogen oxides at typical combustion temperatures indicates that the two most stable oxides are N O and NO? with the former species being predominant. This is also borne
To whom correspondence should be addressed. Volume 6, Number 8, August 1972 727
