Cadmium in Shellfish in Adelaide Central Market - Report Example

www.academia-research.com Sumanta Sanyal d: 06/05/07 Report: Levels of Cadmium in Mussels and Scallops available in Adelaide Central Market Abstract Shellfish - mussels and scallops - were collected from Adelaide Central market and subjected to digestion experiments with nitric and hydrochloric acids to sample cadmium content in them after subjection to an atomic absorption spectrometer. The means (g/g shellfish tissue) for scallops were 0.457 while that for mussels were 0.164. Five samples of each type of shellfish was used in the experiments. The weekly dietary intake figure for the scallops worked out at 1.5 g/kg for a low body weight (60kg) adult and that for the mussels worked out even lower. It was assumed that 500g of each shellfish was consumed in the week. The figures for both types of shellfish was well within the tolerable limits at 7 g/kg body weight for adults as per WHO and Australian guidelines. Nevertheless, since there was observed high standard deviation among the scallop samples and there was also high deviation between the scallop and mussel cadmium/body-weight ratios it has been suggested that a future experiment be conducted during which the origin of the two types of shellfish be ascertained first to ensure that water contamination levels for both types of shellfish are the same. This shall ensure better conformation among the results. Correlation analysis was not conducted because of the small number of samples. This too should be rectified in future experiments to ascertain how each type of shellfish responds to the same level of cadmium contamination in the water. Thus, the report finds that it is highly essential to ascertain contamination in particular harvesting areas so that only those areas from where the bivalves have tolerable metal contents can be allowed harvestable. Other non-conforming areas should be declared out-of-limits. Only this can assure safety in supply. Table of Contents: Introduction Materials and Method Results Discussion Conclusion References 1. Introduction: Cadmium is a heavy metal that is commonly found in many types of soil and rocks. At birth, primates like humans have no cadmium in their bodies but, with age, some humans induct the metal from their environment. The metal is a contaminant and classified as possibly carcinogenic under World Health Organisation (WHO) guidelines (CHEC, Cadmium, 2007). The metal is variously used in industrial applications and commonly found in everyday use objects like paints, plastics, some types of coatings, batteries and other electrical components (CHEC, Cadmium, 2007). The metal is also let out into the atmosphere from burning fuels, especially fossil fuels. It is present in rubber tires and is emitted when tires burn. Also, many industries let out the metal into the atmosphere trough flue gases (CHEC, Cadmium, 2007). Another significant source of cadmium contamination is tobacco smoke. Children are especially susceptible to the metal if they are near smokers (CHEC, Cadmium, 2007). Children also are more prone to cadmium contamination because ration of the metal intake by body weight is much higher than in adults with larger body weight. Thus, more care has to be taken to preclude such contamination in children. Also, it is estimated that cadmium build-up in the body is faster in the early years than later if the individual is subjected to such contamination (WHO, Cadmium, Series 24, 1972). In this particular context it is noted that shellfish like mussels and scallops are bottom-dwellers and are non-mobile filter feeders (Moffett, 1993). In all likelihood, if the metal becomes evident in seawater, it settles down towards the bottom and the shellfish induct it into their systems. Since there is evidence that the metal is not easily evicted from organic tissues. Over time the metal may accrue in shellfish tissue and if these are ingested by humans poisoning may result if the metal levels in the tissue are high enough. Cadmium is nephrotoxic, tending to accumulate in the waste-generating organs like liver and kidneys. In these organs, the metal tends to be bound to a low molecular weight protein metallothionein (WHO, Cadmium, Series 4, 1972). Similar low molecular weight cadmium-binding proteins are also evident in other species like mice. Though metallothionein is present in very low quantities in plasma its low molecular weight (6000-7000) allows it to pass as a metal complex through the filter system of the glomeruli. That explains its large presence in the renal cortex (WHO, Cadmium, Series 4, 1972). Cadmium is also highly implicated in tumourogenesis and carcinogenesis in fowl, mice, rat and humans (Datta et al, 2001). In particular, like other contaminating metal complexes, cadmium complexes are also believed to be involved highly in mutagenesis, effecting changes in genetic structure and function (Datta et al, 2001). In particular relation to shellfish, cadmium intake can range within 13-35 g/day or 0.2 to 0.7 g/kg body weight for adult persons (WHO, Cadmium, Series 24, 1972). The provisional tolerable dietary intake figure set by WHO (1972 estimates) is 1g/kg body weight per day continuously for 50 years (WHO, Cadmium, Series 24, 1972). Therefore, provisional figures set for weekly intake is 7 g/kg body weights for adults (WHO, Cadmium, Series 24, 1972). This figure is subject to the estimation that renal cortex concentrations of the metal does not exceed 50 g/g where the assumption is that the absorption rate is 5% with daily excretion of 0.005% of body burden (WHO, Cadmium, Series 24, 1972). The Australian National Pollutant Inventory (NPI) ranks cadmium and its compounds as 6 out of 400. Total hazard status taking into account both human health and environmental criteria is 4.3 (DEWR, Cadmium, 2005). For human health with hazard rating at 0-3 cadmium and its compounds register 2.3. 3 represents high hazard, 2 medium and 1 harmful to health (DEWR, Cadmium, 2005). For environmental criteria hazard rating at 0-3 cadmium and its compounds register 2 where 3 is highly hazardous and 0 of negligible harm (DEWR, Cadmium, 2005). The Australia New Zealand Food Authority has determined that the principal means of cadmium contamination, other than occupational, is dietary. The tolerance levels are at par with WHO guidelines at 7 g/kg body weights for adults mean weekly though area uptake figures for the same period is deemed at as low as 3.5g/kg body weight (Queensland Health, Undated). It is also notified that shellfish contain more cadmium levels than other foods but, since they are consumed in low quantities comparatively, the authorities pre-suppose no alarm (Queensland Health, Undated). 2. Materials and Method: A number of scallops and mussels were purchased from the Adelaide Central market to investigate what levels of cadmium was present in them. The usual method for sampling cadmium levels present in such shellfish tissues is the digestion method (Moffett, 1993). The exact methodology is stated as hereafter. One mussel, one scallop and a blank were used in the experiment. The shellfish were dried with a paper towel, weighed and their weights recorded. They were next put in labelled 200 ml beakers. 20 ml and 10 ml HCl was put in each beaker together with 2-3 boiling chips. The beakers were put under fume hoods. The same was done for the blank. Watch glasses were put on each beaker and they were placed on a hot plate to boil while still in the fume hood. The beaker contents were stirred every few minutes by gently swirling. Whenever foam was produced the beakers were taken off the hot plate and the watch glasses taken off till the fumes subsided. This went on for 45 minutes till the contents were estimated to have come to a boil. The beakers were removed from heat and allowed to cool. The contents were topped up to 50 ml with distilled water in a volumetric flask, with the blank being done so first. The digests were put into three labelled centrifuge tubes and afterwards put in the Atomic Absorbances spectrometer to determine cadmium levels in each of the three. Note: The blank was taken to estimate the level of cadmium in the contents of the beaker other than the shellfish - the acids, chips, the equipment, etc. Also, this was the reason why the blank was first topped with distilled water in the volumetric flask. This last was to assist in accurate estimation of cadmium levels in the experimental environment. The boiling chips were added to assist in boiling without exploding the beakers during the process. The chips usually assist in even distribution of heat during the process. Various team members repeated the experiment five times and, thus, five sampling results are available. For each mussel and scallop cadmium content result, the total cadmium content in the blank was subtracted from the total metal contents in scallops and mussels. Statistical analysis was done on the results and mean values derived to ascertain whether, on an average, scallops and mussels available in Adelaide Central market conform to cadmium content tolerance levels as prescribed by Australian and World Health Organisation (WHO) norms. 3. Results: Table 1: Cadmium Concentrations: g/g shellfish tissue Sample No. Scallop Mussel 1 0.246 0.186 2 0.418 0.196 3 0.39 0.14 4 0.78 0.19 5 0.45 0.11 Note: The samples are arranged randomly and it is easily noticeable that the cadmium levels found in scallops do not correlate meaningfully with that found in mussels for each experiment. Table 2: Statistical Parameters Scallops Mussels Mean 0.457 0.164 Mode 0.78 0.196 Standard Deviation 0.197 0.038 Note: The number of samples is too small to conduct correlation analysis. It is also notable that the standard deviation for scallop cadmium levels is much higher than that of the mussels. This may suggest that the scallops had not all been collected from the same harvesting waters. There is also a dissimilarity between scallop cadmium levels and mussel cadmium levels suggesting that not all the bivalves have been collected from the same harvesting waters. Graph 1: x-axis: Sample Number y-axis: Cadmium (g/g shellfish tissue) Note: The slopes are meaningless in this instance as the samples have no meaningful sequence though the slopes do point towards how scallop metal levels and mussel metal levels are distributed along the various samples. It is observable from the slopes that mussel metal levels have a much lower standard deviation than that of the scallops. 4. Discussion: It is clearly evident from Table 2 that cadmium content in scallops is much higher than in mussels. It is noted here that both scallops and mussels are bivalves and it has been observed that bivalve molluscs tend to accumulate heavy metals less than other types of molluscs (Eisler, 1998). It has also been observed that mussels are even less likely to accumulate heavy metals because they regulate exposure by reducing survival rates. Thus, the figures available from the experiments demonstrate this fact. The scallops have greater amounts of the metal per body weight than the mussels, which tend to regulate metal retention with survival strategies. A greater retention ratio means less likely chance of survival. Thus, it is likely that mussels with greater amount of the metal in their bodies are unlikely to have survived to the harvesting stage. It is found that the standard deviation for metal retention per unit body weight in scallops is much higher than for the mussels. Together with the low metal retention ratios, this means that the mussels are better at keeping cadmium out of their bodies than the scallops. It is also observed that the metal content is very low per unit body weight and since mussels and scallops are very small food animals there is very little likelihood that the tolerance figures per week at 7 g/kg body weight can be exceeded. The mean for scallops is 0.457 g/g shellfish tissue. Assuming a 500g weekly intake of shellfish, the metal dietary intake is just above 91.4 g for an adult person. Assuming a very low body weight of 60 kg the intake per week works out at 1.52 g/kg body weight. This is well within the WHO and Australian authority recommended figures. The figure for mussels will be even lower. The maximum safe dietary intake of scallops would be 2 kg/week while that for mussels would be 6 kg/week. Conclusion While apparently it seems that the metal content in both types of bivalves are well within permissible limits certain other measures have to be taken to completely assure of this. Firstly, since there is high standard deviation for the scallop cadmium/body weight ratios among the five samples and large differences between the figures for the two types of shellfish it is suggested that future experiments be conducted first ascertaining if both types of shellfish have been harvested from the same area so that it is assured that the water contamination levels for all the samples is the same. This uniformity of data may later reveal noticeable correlation between scallop metal levels and that of mussels always keeping in mind that the mussels are unlikely to allow large accumulation of the metal in their bodies comparative to the scallops. This is as per studied literature (Eisler, 1998). Secondly, since the modal value of the scallop figures is very high the recommended safe limits for both types of bivalves should also be lowered before such future experiment is conducted to exactly ascertain what the actual figures are for shellfish harvested from one area. This last can also ensure supply from only those areas where the bivalves are safe enough for consumption. Areas that are highly contaminated and harvested bivalves have high metal content can be declared off-limits for such harvesting. This again will assure safety in supply. References: Cadmium and compounds factsheet, Department of the Environment and Water Resources (DEWR), Australian Government, 2005. Cadmium, Children's Health Environmental Coalition (CHEC), 2007. Extracted on 2nd May, 2007, from: http://www.checnet.org/healthehouse/chemicals/chemicals-detail-print.aspMain_ID=369 Cadmium, WHO Food Additives Series, 1972, Series 24. Extracted on 2nd May, 2007, from: http://inchemsearch.ccohs.ca/inchem/jsp/search/search.jspinchemcasreg=1&Coll=inchemall&serverSpec=charlie.ccohs.ca%3A9900&QueryText1=&QueryText2=Cadmium&Search.x=0&Search.y=0 Datta, Swapna S., et al, Comparative efficacy of two microdoses of potentized homeopathic drug, Cadmium Sulphoricum, in reducing genotoxic effects produced by cadmium chloride in mice: a time course study, BMC Complementary and Alternative Medicine, 2001, 1:9. Eisler, Ronald, Copper Hazards to Fish, Wildlife, and Invertebrates: A Synoptic Review, Patuxent Wildlife Research Center, U.S. Geological Survey, Laurel, MD 20706, Contaminant Hazard Review: Report No. 33. Evaluation of Mercury, Lead, Cadmium and the Food Additives Amaranth, Diethylpyrocarbonate and Octyle Gallate, WHO Food Additives Series, 1972, Series 4. Extracted on 2nd May, 2007, from: http://inchemsearch.ccohs.ca/inchem/jsp/search/search.jspinchemcasreg=1&Coll=inchemall&serverSpec=charlie.ccohs.ca%3A9900&QueryText1=&QueryText2=Cadmium&Search.x=0&Search.y=0 Moffett, Jonathan H., Analysis of Shellfish tissue for cadmium, mercury and nickel, Varian Instruments Group, 1993. Extracted on 1st May, 2007, from: http://www.varianinc.com/image/vimage/docs/products/spectr/aa/atworks/aa112.pdf Queensland Health, Cadmium, Public Health Guidance Note, Undated. Read More