Geographic variation in hematological variables in adult and prefledgling herring gulls (Larus argentatus) and possible associations with organochlorine exposure

The objectives of this study were (1) to describe variation in hematologica l values found in adult and prefedgling herring gulls (Larus argentatus) ov er a large geographic area, (2) to investigate relationships between hemato logical variables and other physiological indices, and (3) to examine poten tial associations between exposure to organochlorines and hematological var iables. During 1991-93, we sampled 160 breeding adult gulls from 13 colonie s and 101 4-week-old gulls from 11 colonies. All colonies were in the Great Lakes ecosystem, except for two colonies on Lake Winnipeg and the Atlantic coast. The hematological values measured in this study were similar to pub lished values for herring gulls and related species. Significant intersite differences were found in hematological variables. Sex had little or no inf luence on leukocyte variables. Adults had lower total leukocyte counts and higher heterophil to lymphocyte ratios than chicks. PCV was lower in adult females than males. In adults, total leukocyte and total heterophil numbers were negatively associated with liver activity of ethoxyresorufin-O-deethy lase (EROD) and concentrations of highly carboxylated porphyrins (HCPs), tw o biomarkers of organochlorine exposure. Total leukocyte and total heteroph il numbers were positively associated with liver concentrations of DDE (1,1 -dichloro-2.2-bis(p-chlorophenyl)ethyl ene), and total lymphocytes were as sociated positively with PCB (polychlorinated biphenyl) and HCP concentrati ons. The heterophil to lymphocyte ratio was negatively associated with live r EROD activity and HCPs. In chicks, there was a positive association betwe en the heterophil to lymphocyte ratio and HG-TEQs (dioxin toxicity equivale nts calculated usings herring gull-specific equivalency factors). PCV was a ssociated with some measures of contaminant exposure in adults and chicks. Additional research is needed to elucidate causal relationships between hem atological indices and such factors as contaminants, disease, and nutrition .