Analysis Water Quality Monitoring and Human Health


for micrograms per liter. There are 1,000 micrograms in a milligram. Ug/l are the same as ppb or parts per billion. How much is a mg/l or ppm anyway? One ppm is equivalent to one drop of water diluted into 50 liters, which is about the fuel tank capacity of a compact car. A part per billion is equivalent to 1 drop of water diluted into 250 chemical drums filled with liquid. Although these are indeed small numbers, certain contaminants can be harmful to human health if they are present in the parts per trillion, or even present at all.


Toxicity


Would you rather consume a teaspoon or sugar or a teaspoon of dioxin with your morning coffee? Different chemical compounds have different degrees of toxicity. A teaspoon of sugar won’t do you much harm; a teaspoon of dioxin will! So, for example, look at the table below. Phosphorus and arsenic are both present at concentrations of 0.2 mg/l.


Chemical Amount (mg/L)


Phosphorous 0.2 Arsenic


0.2


In fact, both phosphorus and arsenic in this example are present at more than 20 times an acceptable level. However, arsenic is far more toxic than phosphorus and would pose a far greater human health risk. The relative toxicity of different chemical compounds is determined by a number called the LD50. The LD50 is the “lethal dose,” of the chemical that kills 50% of the lab animals exposed to it. This is a rough, not a perfect way, to compare toxicity of different chemicals. For example, in the table you can see how much salt it takes to kill 50% of the rats compared to how much arsenic, dioxin and other substances it takes.


Sugar Salt


Caffeine Nicotine Arsenic Dioxin


Chemical Means of exposure, Animal Oral, rat Oral, rat Oral, rat Oral, rat Oral, rat Oral, rat


LD50 (mg/kg)


29,700 3,000 192 50 13


0.02


Page 60


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117