|Risk Assessment of Lake Sediment – contaminated by chemicals deposited from the ambiance|
|Environmental ToxicologyTable of Contentss|
1Introduction2Methodology2.1Sampling and Analysis2.2Assessment Standards2.3Assessment Methodology3Results4Discussion5Conclusions6References
List of Tables
Table 1 Consensus based likely consequence concentrations ( MacDonald et al. , 2000 )Table 2 The toxicity quotient ( TQ ) values for for Hg, Pb, Cu, Ni, Zn, Cd, and As and Total DDTs, Total PCBs, Total PAHs in the surficial deposit of 10 lakes in the UK and Ireland.
List of Figures
Figure 1 Location of 10 lakes in the UK where the deposit were collected
Sediment was collected from so lakes in the UK that represented the scope of taint by chemicals deposited from the ambiance. This study presents the consequences of the appraisal of the hazard of toxicity from quicksilver ( Hg ) , Lead ( Pb ) , Cu ( Cu ) , nickel ( Ni ) , zinc ( Zn ) , Cd ( Cd ) , and arsenic ( As ) and the organochlorine pesticides entire DDTs ( amount of DDT, DDD and DDE ) , entire polychlorinated biphenyls ( PCBs ) , entire polycyclic aromatic hydrocarbons ( PAHs ) in lake deposit.The chief purposes of the appraisal were to:
- Choice Sediment Quality Guidelines ( SQGs ) for heavy metals and groups of DDTs, PCBs and PAHs in fresh water deposit and place a suited standard for hazard ;
- Calculate toxicity quotients and the average Sediment Quality Guideline Quotient ( mSQGQ ) for heavy metals, DDTs, PCBs and PAHs ; and
- Assess the hazards of toxicity from heavy metals, DDTs, PCBs and PAHs in lake deposit.
- Sampling and Analysis
Sediment was collected from 10 lakes in the UK that represented the scope of taint by chemicals deposited from the ambiance and the upper 5 centimeter of deposit was removed.
The locations of the lakes are shown in Figure 1. Approximately 0.5 g samples of dry deposit were digested with hydrofluoric, azotic and perchloric acids and the concentration of Pb, Cu, Ni, Zn and Cd determined by fire atomic soaking up spectroscopy. Arsenic was determined by ICP-MS and Hg by the cold vapor technique. Approximately 100 g of deposit was freeze dried and extracted with methylene chloride, and organochlorine pesticides, PCBs and PAHs determined by GC-MS, with separate killing processs for each of the three groups of organic chemicals. No atom grain size analysis were carried out.
MacDonaldet Al.( 2000 ) developed consensus based Sediment Quality Guidelines ( SQGs ) for fresh water deposits based on an merger of the published SQGs for fresh water deposits. They classified the SQGs into two classs for each contamination, including a threshold consequence concentration ( TEC ; below which inauspicious effects are non expected to happen ) and a likely consequence concentration ( PEC ; above which inauspicious effects are expected to happen more frequently than non ) ( MacDonaldet Al., 2000 ) .
Table 1 shows the selected consensus-based PECs from MacDonaldet Al.( 2000 ) were used to measure whether the reported values for Hg, Pb, Cu, Ni, Zn, Cd, and As and Total DDTs, Total PCBs, Total PAHs, in the fresh water deposit samples were toxic or non.Table 1 Consensus based likely consequence concentrations ( MacDonald et al.
, 2000 )
|Parameter||Metallic elements||EntireDichlorodiphenyltrichloroethane||Entire PCBs||Entire PAHs|
|Unit ( per DW )||µg/g||µg/g||µg/g||µg/g||µg/g||µg/g||µg/g||ng/g||ng/g||ng/g|
|Consensus Based PEC values||0.18||35.8||31.6||22.7||121||0.99||9.
- Calculation of Toxicology Quotient
The toxicity quotient is the concentration in the sediment sample divided by the SQG value and is known as the Sediment Quality Guideline Quotient ( SQGQ ) . Longet Al.( 2006 ) describes the methodological analysis for ciphering the average SQGQs in a three-step procedure. First the SQGQ was calculated for each metal ( Hg, Pb, Cu, Ni, Zn, Cd and As ) and for the undermentioned group of chemicals Total DDT, Total PCBs and Total PAHs.
The following measure was to cipher the mean of the toxicity quotients of all the metals ( Metals-SQGQ ) . Finally, cipher the mean of the toxicity quotients for Metals-SQGQ, DDT-SQGQs, PAHs-SQGQ and PCBs-SQGQ was calculated. This concluding overall quotient is called the mean deposit Quality Guideline Quotient ( mSQGQ ) . The mSQGQ is a “individual, unitless, consequence based index of the comparative grade of taint that can supply a footing for finding the likeliness that a sediment sample would be toxic to sediment-dwelling beings” ( Longet Al. , 2006 ) .Two average toxicology quotients were calculated for each lake following an attack used in Ingersollet Al.
( 2001 ) . The first used the 7 single metals and the Total DDT, Total PCBs and Total PAHs. This was done by summing the toxicology quotients and so spliting by 10 to give the average toxicology quotient. This was referred to as mSQGQ ( individualM ) , this weighs all chemicals and chemical categories every bit ( Ingersollet Al., 2001 ) . The 2nd average toxicology quotient was calculated by summing the Metals-SQGQ, and the toxicity quotient for Entire DDT, Total PCBs and Total PAHs.
This was referred to as mSQGQ ( meanM ) and this method gives equal weighting to each group of chemicals ( Ingersollet Al., 2001 ) .Note that where the reported values were less than the method sensing bound, half the sensing bound was used when ciphering the toxicity quotient.
This helps to guarantee that non-detect values are non under or overestimated during the appraisal of hazard.
- Toxicity Quotient Assessment Methodology
A toxicity quotient of & gt ; 1.0 was be chosen as the threshold, when utilizing the PEC value to measure each poison individually. This was based on Table 5 in MacDonaldet Al.( 2000 ) which provides the proportion of samples with a toxicity quotient greater than one, that were found to be toxic in ecotoxicity trials. The values varied from 76.
9 to 100 % for the relevant chemicals or groups.For single metals, to measure whether there were any major exceedances of the PEC an extra threshold of & gt ; 5.0 ( Ingersollet al.
,2001 ) was chosen as it was considered to bespeak higher hazard of toxicity to deposits, as the metal would be 5 times greater than the consensus-based PEC.A toxicity quotient threshold of & gt ; 0.5 was chosen for measuring the average toxicity quotient. MacDonaldet Al.( 2000 ) concluded that a average PEC quotient of 0.5 represents a utile threshold that can be used to accurately sort sediment samples as both toxic and non toxic.
Ingersollet Al.( 2001 ) besides found that in all toxicity trials at that place was a consistent addition in the toxicity of samples with average toxicity quotients & gt ; 0.5.
Table 2 nowadayss the consequences of the toxicity quotient computations for the seven single metals, metals as a group, Total DDTs, Total PCBs and Total PAH and for the average toxicology quotients ( mSQGQ ) .
The consensus-based PEC values of MacDonaldet Al.( 2000 ) as shown in Table 1 were used.Table 2 The toxicity quotient ( TQ ) values for Hg, Pb, Cu, Ni, Zn, Cd, and As and Total DDTs, Total PCBs and Total PAHs in the surficial deposit of 10 lakes in the UK.
|Toxicity Quotients||Lakes||Agden Reservoir||Burnmoor Tarn||Llyn Cwm Mynach||Llyn Llagi||Loch Chon||Loch Coire Fionnaraich||Loch Doilet||Lochnagar||Scoat Tarn||Honking Common Lake|
|Individual metals SQGQNote 1 & A ; 2:|
|Group SQGQNote 1:|
|Mean SQGQsNote 2:|
|mSQGQ ( individualM )||2.25||1.23||2.25||1.56||1.61||0.29||0.
|mSQGQ ( meanM )||0.892||0.442||0.837||0.
- For single metals SQGQ and group SQGQ the ratios & gt ; 1 are bolded. This shows an exceeded of the consensus based PEC.
- For single metals SQGQ the ratios & gt ; 5 are bolded and in italics.
- For average SQGQ the ratios & gt ; 0.5 are bolded.
SQGQ – Sediment Quality Guideline QuotientEntire DDTs are the amount of DDT, DDD and DDE
- Individual Toxicology Quotients
All of the lakes sampled were at hazard from one or more metals with the toxicity quotient for single metals greater than 1.0, runing from 40 to 90 % of the 10 lakes. Pb was the metal which the lakes were at the greatest hazard from as 90 % had a toxicity quotient of greater than 1.
0. Hg was the metal the lakes were at the following greatest hazard from, as 80 % had a toxicity quotient of greater than 1.0, so followed by As with 70 % , Cd with 60 % , Zn with 50 % and eventually Cu and Ni where 40 % of the lakes had a toxicity quotient of greater than 1.0. Overall for all of the sites the exceedance ranking was Pb so Hg, As, Cd, Zn, and eventually Cu and Ni.SQGQs can be used to prioritize lakes that are of possible concern by assisting to place the lakes with the greatest exceedance of the PECs in footings of magnitude and for the most sum of chemicals ( Chapmanet Al., 1999 ) .
It was calculated that overall for all of the lakes and metals there were 61 % cases of exceedances of the PECs as shown in Table 2. Thirty four per centum were comparatively little exceedances with ratios between 1.0 and 2.0. There were besides some major exceedances and in order to quantify this a threshold of & gt ; 5.
0 for an single metal was used ( i.e. 5 times greater than the consensus-based PEC ) . The metals with the toxicity quotient for single metals greater than 5.0 were Pb in 40 % of lakes, As in 30 % of lakes and Cd in 10 % .
The mean toxicity quotient for all the metals in the deposit of each lake sample was calculated ( Metals-SQGQ ) . All the lakes had a Metals-SQGQ of greater than 1.0, with the exclusion of Loch Doilet ( Metals-SQGQ 0.757 ) and Loch Coire Fionnaraich ( Metals-SQGQ 0.413 ) .
The lake with the highest Metals-SQGQ was Scoat Tarn with a value of 3.90, even though merely four metals exceeded the PECs. Pb and As were peculiarly elevated with toxicity quotients of 11 each. This indicated that the sample from Scoat Tarn has the highest hazard of toxicity from metals in deposits.The SQGQ was besides calculated for each of the other chemical groups ; Total DDT, Total PCBs and Total PAHs as shown in Table 2. None of the 10 lakes had a toxicity quotient greater than 1.
0 for Entire DDT, Total PCBs and Total PAHs. In fact the toxicity quotients were comparatively low runing from 0.0 to 0.001 for Entire DDT, from 0.001 to 0.015 for Entire PCBs and 0.008 to 0.416 for Entire PAHs.
These low toxicity quotients indicate that all of the lakes are at low hazard from Entire DDT, Total PCBs and Total PAHs in deposits.Contaminant of ConcernThe contamination of concern can be identified by finding the contamination with the greatest figure exceedances of the consensus based PEC ( Chapmanet Al., 1999 ) . The chemical of concern is Pb as deposit in 90 % of the lakes sampled is at hazard from Pb deposited from the ambiance. In add-on the in 40 % of the lakes the Pb toxicity quotient is & gt ; 5.0.Given the high happening of lakes transcending the consensus based PEC for Pb it is recommended that in farther work the Pb degrees should be compared to play down concentrations of Pb, either from samples from mention lakes or by taking a deeper nucleus and analyzing historic lead degrees in the lakes to assist gauge existent Pb taint ( Rose and Rippey, 2002 ) .
- Mean Toxicology Quotients
The consequences of the average toxicology quotients for each lake ranged from 0.
290 to 2.74 for the mSQGQ ( individualM ) . Ninety per centum of the lakes had a mSQGQ ( individualM ) of greater than & gt ; 0.5 bespeaking a high hazard of toxicity in the bulk of the lakes sampled. The lake with the highest mSQGQ ( individualM ) was Scoat Tarn with a value of 2.
74. This lake besides had the highest Metals-SQGQ. Similarly the two lakes with the lowest mSQGQ ( individualM ) were Loch Doilet ( mSQGQ ( individualM ) 0.757 ) and Loch Coire Fionnaraich ( mSQGQ ( individualM ) 0.413 ) , which are both located in the north West of Scotland.The consequences of the average toxicology quotients for each lake ranged from 0.106 to 0.
999 for the mSQGQ ( meanM ) . Merely 60 % of the lakes had a mSQGQ ( meanM ) of greater than & gt ; 0.5. This indicates that less of the lakes are at hazard overall than when the single metals are used for the mSQGQ.
It is hence considered in this case that the mSQGQ ( individualM ) is more representative of the existent hazard of metals toxicity in the deposits because the mSQGQ ( meanM ) is burdening the groups flushing and in making so dissemble the existent exceedances of consensus-based PECs for single metals. The mSQGQ ( individualM ) is hence more conservative as four excess lakes, Burnmoor Tarn, Llyn Cwm Mynach, Loch Doilet and Tooting Common Lake are considered to be at hazard of toxicity in the deposits.
- Spatial Appraisal
Scoat Tarn is located in the Northwest of England had the highest mSQGQ of 2.74. This would non be unexpected as the North of England is known to be more industrial. Burnmoor Tarn is located ( see Figure 1 ) is in close propinquity ( less than 10 kilometer ) to Scoat Tarn and it had a Metals-SQGQ of 1.23 whereas Scoat Tarn had the highest mSQGQ of 2.74.
Given the close propinquity of the lakes it would be expected that the toxicity quotients would be more similar. This difference may bespeak that the metals taint in the deposits in Scoat Tarn may non be merely be from an atmospheric beginning and that something could be happening locally in the catchment, or that a hot spot of taint was sampled. Another factor that could act upon this difference is the atom size of the deposit. Wisconsin Department of Natural Resources ( 2003 ) province that finer deposits can hold higher metal concentrations due to metal surface assimilation and that grain size should be factored in when comparing informations between sites.Loch Coire Fionnaraich appears to be the least wedged site and has a mSQGQ of 0.
29 which is really low and below the toxicity quotient threshold of 0.5. Loch Doilet was the lake with the following highest toxicity quotient of 0.532 which was merely above the threshold. Both lakes are located in the Northwest of Scotland which would be farther removed from industries.
This is consistent with Rose and Rippey ( 2002 ) who say that the Northwest of Scotland is believed to be the least wedged country in the UK.Despite the low concentrations of contaminates observed in the Northwest of Scotland no other spacial form in the informations could be observed at the 10 sites.Page 1