Agricultural Chemicals in Iowa's Groundwater: Tables

Temporal Trends of Selected Agricultural Chemicals in Iowa's Groundwater, 1982-95: Are Things Getting Better?

Dana W. Kolpin, Debra Sneck-Fahrer, George R. Hallberg, and Robert D. Libra

TABLES

Table 1 | Table 2 | Table 3 | Table 4 | Table 5

Table 1. Estimated use of selected agricultural chemicals in Iowa, 1982-95.


                        Average Chemical Use
                        (in 1,000 kg/year of active
Compound                ingredient)

                        1982-86   1987-91   1992-95
-----------------------------------------------------
Nitrogen-fertilizer¹    876,300   836,700   834,200

Alachlor²                 6,260     3,740     2,350

Atrazine²                 3,710     3,380     3,264

Cyanazine²                4,282     2,654     3,170

Metolachlor²              3,059     4,949     4,709

----------------------------------------------------
                        Average Intensity of Use
                        (kg/hectare)

                        1982-86   1987-91   1992-95
-----------------------------------------------------

Nitrogen-fertilizer¹    155       145       132

Alachlor²                 2.26      2.52      2.54

Atrazine²                 1.64      1.08      0.98

Cyanazine²                2.31      2.38      2.53

Metolachlor²              2.69      2.30      2.30

-----
¹ Vroomen, 1989; U.S. Department of Agriculture, 1995
² Hartzler and Wintersteen, 1991; U.S. Department of Agriculture, 1995

Table 2. Summary of results for groundwater samples collected for the Iowa Ground Water Monitoring Program during the months of April to September (1982-95) for selected agricultural chemicals.

[N, number of samples; HA, health advisory level; MCL, maximum contaminant level; mg/L, milligram per liter; µg/L, microgram per liter; HA, health advisory level]

					   Frequency of
			    Reporting	   detection
Compound	N	    limit	      (%) 
-----------------------------------------------------------
Nitrate 	1929        0.10 mg/L	    57.1 
Alachlor 	1485        0.10 µg/L	     3.0
Atrazine 	1485        0.10 µg/L	    19.5
Cyanazine 	1314        0.10 µg/L	     3.6
Metolachlor 	1309        0.10 µg/L	     5.7 
------------------------------------------------------------
					      Frequency of
					      exceedence,
	      Maximum	        MCL or	      MCL, or HA
	      concentration	HA¹		(%)	
------------------------------------------------------------

Nitrate       53.0 mg/L		10 mg/L 	 7.2
Alachlor      14.0 µg/L		 2.0 µg/L 	 0.4
Atrazine      21.0 µg/L		 3.0 µg/L	 0.8
Cyanazine      4.5 µg/L		 1.0 µg/L¹	 0.3
Metolachlor  200 µg/L	       100 µg/L¹	<0.1
-------
¹Health advisory from U.S. Environmental Protection Agency (1996)

Table 3. Temporal patterns in frequency of detection for selected agricultural chemicals in Iowa groundwater (1,019 wells). A P value ± 0.05 is not considered statistically significant.

						
	    Median Frequency of Detection (%)	 Results of
	    ---------------------------------	 Kruskal-Wallis
Compound     1982-86     1987-91     1992-95	 test (P value)

----------------------------------------------------------------
Nitrate	      48.1 	  61.5	      55.4 	 0.229
Alachlor       0.0	   2.2	       3.3	 0.541
Atrazine      15.4 	  19.3	      13.2	 0.152
Cyanazine      0.0	   3.3	       4.1 	 0.096
Metolachlor    0.0	   4.8	      14.1 	 0.009

Table 4. Temporal patterns in frequency of detection for selected agricultural chemicals in Iowa groundwater (1,019 wells) by well depth group. A P value >/= 0.05 is not considered statistically significant.

		Median Frequency of Detection (%)
		---------------------------------
						      Results of Kruskal-
Compound 	 1982-86     1987-91	1992-95       Wallis test (P value)
----------------------------------------------------------------

			  Shallow Wells ( 15 m) (need less than/equal to symbol)

Nitrate 	 77.1 	     81.1 	76.1 		0.292
Alachlor 	  0.0 	      1.4 	 4.0 		0.248
Atrazine 	 20.0 	     29.7 	16.4 		0.027 
Cyanazine 	  0.0	      5.8 	 4.1 		0.163
Metolachlor 	  0.0 	      6.2 	 6.8 		0.480

		       Intermediate Wells (16-30 m) 

Nitrate 	 72.0	     81.2 	76.0 		0.120 
Alachlor 	  0.0 	      3.9 	 1.4 		0.390 
Atrazine 	 19.4 	     25.0 	22.2 		0.431 
Cyanazine 	  0.0 	      6.4 	 8.8 		0.108
Metolachlor 	  0.0 	      7.1 	28.6 		0.006 

			    Deep Wells (>30 m) 

Nitrate 	 36.8 	     40.7 	27.8 		0.254 
Alachlor 	  0.0 	      2.4 	 1.9 		0.344 
Atrazine 	  6.9 	     10.6 	 7.6 		0.361 
Cyanazine 	  0.0 	      1.2 	 0.0 		0.056 
Metolachlor 	  0.0 	      1.3 	 3.4 		0.130

Table 5. Temporal patterns in frequency of detection for selected agricultural chemicals in Iowa groundwater (1,019 wells) by aquifer type. A P value 0.05 >/= is not considered statistically significant.

                Median Frequency of Detection (%)
                ---------------------------------
                                                      Results of Kruskal-
Compound         1982-86     1987-91    1992-95       Wallis test (P
 value)
----------------------------------------------------------------

		      Alluvial Aquifers

Nitrate 	 73.8        79.0 	74.2 		0.309
Alachlor 	  0.0         1.7 	 3.1 		0.797
Atrazine 	 19.2 	     28.3 	21.0 		0.150
Cyanazine	  0.0 	      4.2 	 6.5 		0.165 
Metolachlor 	  0.0 	      7.4 	16.5 		0.023 

		   Glacial-Drift Aquifers

Nitrate 	 46.9 	     57.5 	34.8 		0.214
Alachlor	  0.0 	      3.4 	 0.0 		0.470
Atrazine 	  6.7 	     17.2 	 0.0 		0.094
Cyanazine 	  0.0 	      3.4 	 0.0 		0.062
Metolachlor 	  0.0 	      0.0 	 0.0 		0.927

			   Bedrock

Nitrate 	 39.7 	     47.7 	46.3 		0.505
Alachlor 	  0.0 	      2.5 	 2.2 		0.176
Atrazine 	 20.0 	     14.3 	14.6 		0.823
Cyanazine 	  0.0 	      1.8 	 0.0 		0.023
Metolachlor 	  0.0 	      1.8 	 4.7 		0.130

Next: Figures

Pesticide National Synthesis Project

Temporal Trends of Selected Agricultural Chemicals in Iowa's Groundwater, 1982-95: Are Things Getting Better?

TABLES